Abstract: To select parental lines and sorghum hybrid with high net photosynthesis rate, 18 crossing combinations were made by 3 sterile lines and 6 restorer lines with incomplete diallel cross method. The general combining ability (GCA) effect and special combining ability (SCA) effect of net photosynthesis rate on parental lines and crossing combination were analyzed at heading stage, anthesis stage and grain filling stage. Correlation analysis on net photosynthesis rate and main agronomic characters and yield were carried out. The results showed that the general combining ability of sterile line 162273A was the highest in net photosynthesis rate at heading stage, anthesis stage and grain filling stage, its relative effect value at these three stages was respectively 16.2706, 9.7331 and 11.9907. The general combining ability of restorer line 16727, 161011 and 161026 was the highest in net photosynthesis rate at the three growth stage respectively, with the relative effect value as 10.6624, 23.7309, and 18.0146. The special combining ability of crossing combination 162273A× 16878, 162279A×161026 and 162279A×161026 was the highest in net photosynthesis rate at the three growth stage respectively, with the relative effect value as 35.0123, 19.9455 and 33.0046. The ratio of additive genetic variance to genotype variance was low and the narrow-sense heritability was also low at the three growth stages. Correlation analysis showed that net photosynthesis rate had extremely significant positive correlation with grain weight per spike, 1000 grain weight, grain yield, biomass yield and the harvest index.