[Objective] The aim was to measure photosynthetic characters of SC 205, a cassava cultivar, and explore the relationships of the net photosynthetic rate(Pn) with physiological and ecological factors. [Method] The diurnal variations of photosynthesis in leaves of SC205 were studied by LICOR-6400 portable photosynthesis system, and the relationships of the net photosynthetic rate(Pn) with physiological and ecological factors were studied by simple correlation analysis and path analysis. [Result] The curve of diurnal variation of Pn showed single peak at 10:00 am at 24.07 μ mol CO2m2/s, without showing midday depression; the diurnal changes of stomatal conductance(Gs), transpiration rate(Tr), leaf temperature(Tl), air temperature(Ta) and photosynthetic active radiation(PAR) all showed single peak curves, and there were positive relationships of Pn with Gs, Tr, Tl, Ta and PAR. The diurnal variations of intercellular CO2concentration(Ci), atmospheric CO2concentration(Ca), relative humidity(RH) showed in a U-shape curve. There were highly significant positive correlation of Pn with Gs and PAR; the diurnal variation of Pn had highly significant negative correlations with Ci and Ca. The direct impact of physiological factors on Pn was as follows: Ci>Gs>Tl>Tr, and the direct impact of ecological factors was RH >PAR >Ca >Ta. [Conclusion] The research showed that Ci, Gs and Tr play very important roles in the changes of Pn among the physiological factors, and PAR and Ca affect the changes of Pn among the ecological factors. [Objective] The aim was to measure photosynthetic characters of SC 205, a cassava cultivar, and explore the relationships of the net photosynthetic rate (Pn) with physiological and ecological factors. [Method] The diurnal variations of photosynthesis in leaves of SC205 were studied by LICOR-6400 portable photosynthesis system, and the relationships of the net photosynthetic rate (Pn) with physiological and ecological factors were studied by simple correlation analysis and path analysis. [Result] The curve of diurnal variation of Pn showed single peak at 10: 00 am at 24.07 μ mol CO2m2 / s without showing midday depression; the diurnal changes of stomatal conductance (Gs), transpiration rate (Tr), leaf temperature (Tl), air temperature (Ta) and photosynthetic active radiation showed single peak curves, and there were positive relationships of Pn with Gs, Tr, Tl, Ta and PAR. The diurnal variations of intercellular CO2concentration (Ci), atmospheric CO2concentration (Ca), relative humidity There were highly significant positive correlation of Pn with Gs and PAR; the diurnal variation of Pn had highly significant negative correlations with Ci and Ca. The direct impact of physiological factors on Pn was as follows : Ci> Gs> Tl> Tr, and the direct impact of ecological factors was RH> PAR> Ca> Ta. [Conclusion] The research showed that Ci, Gs and Tr play very important roles in the changes of Pn among the physiological factors , and PAR and Ca affect the changes of Pn among the ecological factors.