Abstract: The aim is to investigate the effect law of planting density on canopy structure and photosynthetic characteristics of medium maturity spring soybean under drip irrigation.‘Xindadou 27’and‘11-109’were used as the experiment materials, and three densities [18.0×104 (D1), 28.5×104 (D2), 36.0×104 (D3)/hm2] were set in the field experiment, and the canopy leaf area index (LAI ), chlorophyll content (SPAD ), net photosynthetic rate (Pn ), dry matter accumulation and yield were determined systematically under different treatments. The results showed that with the density increased from D1 to D2,LAI , dry matter accumulation and yield increased significantly; with the density increased from D2 to D3,LAI continued to increase, while dry matter and yield no longer increased. With the planting density increasing,SPAD andPn of leaves below the seventh joint position decreased significantly, and the podding position was raised. Besides, grain number per plant, grain number and economic coefficient also decreased significantly;‘Xindadou 27’was not sensitive to density change compared with‘11-109’onLAI , dry matter accumulation andPn . D2 was the suitable density for the two varieties (strains) of spring soybean, the grain yield of‘Xingdadou 27’was 5551.13 kg/hm2, which was 14.73% higher than that of‘11-109’. The responses of canopy structure, photosynthetic characteristics and yield of super-high yield varieties to planting density were not as sensitive as those of high yield varieties.