Abstract: This study was aimed to investigate the appropriate light conditions for Juglans mandshurica saplings of different ages, and provide a theoretical basis for the development of artificial tending measures for J. mandshurica saplings in the understory. In this study, natural regeneration of J. mandshurica saplings aged 1-3 a（age stage Ⅰ）, 4-6 a（age stage Ⅱ） and 7-9 a（age stage Ⅲ） in the experimental forestry farm of Zhuan Shan, Fangzheng County, Harbin City were used as experimental subjects, determining their growth patterns and photosynthetic indicators in different light environments（forest edge, forest gap and understory）. The results showed that: as light intensity diminished, the biomass, saplings height and ground diameter decreased, and the specific leaf area increased; chlorophyll a/b, light compensation point（LCP）, the highest maximum net photosynthetic rate(P_max) and dark respiration rate（R_d） decreased, chlorophyll content increased in saplings of all ages. In the understory and the forest gap, saplings of age Ⅱ had the highest maximum net photosynthetic rate and chlorophyll content and the lowest values of light compensation point, dark respiration rate and chlorophyll a/b; the highest maximum net photosynthetic rate and light compensation point of saplings increases as saplings age in the forest edge. In summary, the forest edge is more suitable for the growth of saplings. In addition, when artificially tending J. mandshurica saplings between 4 and 6 years old, tending intensity can be reduced appropriately. In contrast, when artificially tending J. mandshurica saplings of 1-3 and 7-9 years old, and light transmittance of the upper forest layer should be strengthened timely.