Abstract: In order to improve the yield of soybean, find the suitable planting density and explore the regulation effect of mepiquat chloride on the yield of soybean, the soybean variety Laidou 2 was selected, and the seedling density was set as 2.00×10~5 plants·ha^-1（D20.0）, 2.25×10~5 plants·ha^-1（D22.5） and 2.50×10~5 plants·ha^-1（D25.0）. The effect of spraying mepiquat chloride on the yield and quality of soybean under different densities was studied. The results showed that the plant height of D22.5+DPC and D25.0+DPC treatment was significantly lower than that of the corresponding control group. The number of effective pods per plant in D25.0+DPC treatment increased compared with the control group, and the number of grains per plant and 100-seed weight increased significantly compared with the control group. The yields of D20.0+DPC,D22.5+DPC and D25.0+DPC were significantly higher than those of the corresponding control groups, and the fat content increased by 0.19%-0.67%. The yield-increasing effect of spraying mepiquat chloride was the best when the seedling density was 2.50×10~5 plants·ha^-1.