Photosynthesis is the basis of other physiological activities including growth, development, and food formation in trees. In order to discuss the photosynthetic theoretical basis for the cultivation of Robinia pseudoacacia L. energy forest, the photosynthetic parameters, i.e. Pn, Tr, Gs, etc, as well as photosynthetic light-response curves of 5 varieties of Robinia pseudoacacia were measured using the Li-6400 portable photosynthesis system in the west of Henan Province, China. Four main conclusions were gotten. The peak value of net photosynthetic rate (Pn) of 5 varieties of Robinia pseudoacacia occurred at noon, 08:00 or 10:00 a.m., 10:00 a.m. in mid-July, mid-August and late September respectively. Obvious difference existed among growth dynamics of 5 varieties, and varieties 83002, 8048 and 8044 showed fast growth rate in July, while variety 3-I grew fastly in September. Varieties 84023, 3-I and 83002 were found having relatively high photosynthetic accumulation capacity and had the high-yield photosynthetic characteristics. Based on the tendency of changes in Pn, intercellular CO2 concentration (Ci), stomatal conductance (Gs) and stomatal limitation (Ls), we speculated that Robinia pseudoacacia were restricted in photosynthetic ability mainly by non-stomatal factors in mid-July, while they were restricted mainly by both stomatal factors and non-stomata factors in mid-August and the end of September. Light is the power in photosynthesis. Light compensation point is a critical value, over this value plant still can maintain photosynthesis. Light saturation point is a limit value, over this value photosynthetic rate does not increase, even decrease. Light saturation point (LSP) of Robinia pseudoacacia varieties were all greater than 1000μmol?m-2?s-1, and so, these tested varieties all could not suffer restriction from strong light occurred in mid-July. Photosynthesis is related to temperature, light radiation and CO2 concentration, which are necessary to valuate photosynthetic capacity. Except variety 83002, net photosynthetic rate (Pn) of other four varieties of Robinia pseudoacacia had only one peak, only variety 83002 had two peaks, one at 10:00 a.m. and the other at 02:00 p.m. Transpiration rate (Tr) of varieties 83002 and 84023 had two peaks, the others had one peak only. The phenomenon of “photosynthesis sleep at noon” of variety 83002 might be explained as the combined result of both increment in temperature and drop of relative humidity. It was suggested that in order to estimate photosynthetic accumulation capacity and select one quality variety, the photosynthetic characteristics of varied cultivars of Robinia pseudoacacia L.energy forest could be analyzed.