Abstract: To investigate the effects of different harvest time on silage quality of silage maize in Western Guangdong Region and the effects of different proportions of silage maize and pineapple residue combinations on in vitro fermentation parameters, a randomized block design in the experiment was adopted with a total of three plots. Representative plants were selected for marking in the early growth stage of silage maize. From the 25 th day after stamen flowering, 6 plants were randomly selected from each plot every 4 days for 8 consecutive times. They were divided into D1（the 25 th day after stamen flowering）, D2（the 30 th day after stamen flowering）, D3（the 35 th day after stamen flowering）, D4（the 40 th day after stamen flowering）, D5（the 45 th day after stamen flowering）, D6（the 50 th day after stamen flowering）, D7（the 55 th day after stamen flowering） and D8（the 60 th day after stamen flowering） groups. After measuring the agronomic traits of each group, the plants were sealed with vacuum bags and silaged for 90 days. At the end of silage, the fermentation quality and nutrient composition of each group were determined. Three groups of silage corn with relatively good agronomic traits and silage quality were selected and mixed in equal proportion. Then it was mixed with silage pineapple residue in different ratios（0∶100, 25∶75, 50∶50, 75∶25, 100∶0）, and fermented in vitro after adding fermentation broth. Each ratio was set for 4 fermentation times（3, 12, 24, 48 h）. Three replicates were set for each ratio and each fermentation time. After fermentation, the pH value and volatile fatty acid content in vitro were measured. The results showed that plant height and grain weight of silage maize generally showed an increasing trend with the extension of harvest time, and stem weight and ear weight increased first and then decreased, while the number of green leaves and total leaf area decreased. The stem weight of groups D4, D5, and D6 was significantly higher than that of the other groups（P＜0.05）. The panicle weight of groups D3 and D4 was significantly higher than that of the other groups（P＜0.05）, and the stem weight and panicle weight of group D4 were the highest. The pH value of each group after ensiling was less than 4.2. With the prolongation of harvest time, the content of WSC in each group showed an increasing trend after silage; the content of lactic acid and acetic acid showed a trend of increasing first and then decreasing, and there was no significant change in NH3-N. The content of WSC in groups D6, D7 and D8 was significantly higher than that in other groups（P＜0.05）. The content of lactic acid in groups D4 and D5 was significantly higher than that in other groups（P＜0.05）, while the content of acetic acid in group D6 was significantly higher than that in other groups（P＜0.05）. With the extension of harvest time, the contents of crude protein, crude fat and crude fiber in each group showed a downward trend; the contents of neutral detergent fiber and acid detergent fiber showed an upward trend, and the contents of calcium and phosphorus did not change significantly. Among them, the crude protein content of D4, D5 and D6 was between 6.78% and 7.16%, the neutral detergent fiber content was between 34.65% and 39.26%, and the acid detergent fiber content was between 19.31% and 24.37%. With the extension of fermentation time, the pH value of all proportions of silage corn and silage pineapple residue combinations showed a downward trend, but there was no significant difference in pH value of all proportions of silage corn and silage pineapple residue combinations at the same fermentation time（P＞0.05）. When the fermentation time was 12-48 h in vitro, the pH values of the combination of silage corn and silage pineapple residue in all proportions were between 6.44 and 6.88. With the extension of fermentation time in vitro, the contents of acetic acid, propionic acid and butyric acid in the combination of silage corn and silage pineapple residue of all proportions increased first and then decreased. When the fermentation time was 24 h and 48 h, the content of acetic acid,propionate and butyric acid of the combination of silage corn and silage pineapple residue with the ratio of 75∶25 was the highest, which was significantly higher than that of the other groups（P＜0.05）. The results indicated that the combination of silage corn and silage pineapple residue produced a certain positive combination effect, and the harvest time of silage maize at the 40 th-50 th days after stamen flowering was suitable in Western Guangdong Region, and the combination of silage maize and silage pineapple residue with a ratio of 75∶25 in the late fermentation stage（24-48 h） had the highest content of volatile fatty acids during in vitro fermentation under the experimental conditions.