The photosynthetic characters were observed with CI-340 portable photosynthesis determination system produced by United States.The relationships of P_n and eco-physiological factors were analyzed with path coefficient and the light-response curve was fitted with parabola model for Caryota urens and Caryota mitis.The results showed as follows:(1)The net photosynthetic rate of two species presented asymmetric double peak curve,with a clear “midday depression”,and its length and depth in C.urens was more obvious than that in C.mitis,and the minor peak in C.urens was also delayed about 2 hours.These differences maybe result from the various activities of physiological factors such as stomatal conductance and transpiration rate and so on.(2)C_i is the main physiological factor affecting the characteristic of P_n of two species.However,G_s was the main limiting factor in C.urens,Tleaf in C.mitis;The main ecological factor was PAR in C.urens,C_air in C.mitis and RH was the limiting factor of two species.(3)The light-response curve of two species was fitted with parabola models.The high LCP (light compensation point) and LSP (light saturation point) in two species showed that they all belonged to strongly light plant.However,these values were higher in C.urens than that in C.mitis.Thus,the latter was more adaptive to be removed from south to north.