The influencing factors of leaf net photosynthetic rate (Pn) in different growth stages and leaf position under greenhouse condition were studied by analyzing the dynamic characteristic of photosynthetic characteristic and the correlation between Pn and the eco-physiological factors based on the Water Transformation Dynamical Processes Experimental Device (WATDPED). The results showed that there was only one peak of the variations of Pn, chlorophyll content (chl), stomatal conductance (Gs), N content (N) during the growth period. However, the maximum value of Pn, appeared in milk stage, was lower and one growth stage later than the previous research results of fields (the tasseling and silking stage). The Pn, chl and Gs showed higher value in middle leaf positions than in other leaf positions. During the growth period, the correlation coefficient between Pn and chl was the highest (0.94, P<0.05), followed by the coefficient between Pn and N and that between Pn and Gs (0.77, P<0.05). The variation of Pn in different leaf position was similar to that of Gs. The device is more suitable to be used to conduct some control experiment studying the influence of climate change, water and nutrient stress on the crops or ecosystems.