[Objective] The aim was to explore the gases exchange characteristic in leaves of soybean cultivars at different yield levels to provide a certain theories basis for high yield breeding and cultivation of soybean cultivars. [Method] Nine soybean cultivars divided into three yield levels were planted under the same environmental condition. At V4（seedling）,R2（blooming）,R4（pod-bearing）,R6（pod-filling） and R7（maturing） growth stages,the net photosynthetic rate （Pn）,stomatal conductance （Gs） and transpiration rate （Tr） in soybean leaves were measured with Li-6400 portable photosynthesis system. [Result] At all growth stages,the net photosynthetic rate,stomatal conductance in leaves of high yield soybean cultivars were significantly higher than low yield soybean cultivars. At V4,R2 and R4 stages,transpiration rate in leaves of high yield soybean cultivars was significantly higher than low yield soybean cultivars; there was no significant difference on transpiration rate in leaves of soybean cultivars at different yield levels at R6 and R7 stage. At V4 and R2 stage,water use efficiency （WUE） in leaves of soybean cultivars at different yield showed a trend of low yield cultivarsmiddle yield cultivarshigh yield cultivars,while it appeared high yield cultivarsmiddle yield cultivarslow yield cultivars at R4,R6 and R7 stage. [Conclusion] The gases exchange capacity in leaves of high yield soybean cultivars was significantly higher than low yield soybean cultivars,which had provided physiological basis of high yield. The net photosynthetic rate could be used as an selection index of high yield soybean.
