To study the physiological characteristics of high light efficiency in cassava cultivar Ku50, W14, a wild type, wild relatives of A4047 and cultivated species of Ku50 were used as the materials to investigate the character of photosynthetic physiology during different varieties of cassava by measuring the photosynthetic pigment content on functional leaves, net photosynthetic rate (including the photosynthetic rate curve under different light intensity and photosynthetic daily variation) and chlorophyll fluorescence parameters (including mainly the actual photosynthetic efficiency of PSⅡ-Y(Ⅱ), and non-photochemical quenching-NPQ). The result showed that the content of various photosynthetic pigments in Ku50 was significantly higher than that in W14, but no significant difference with that in A4047, suggesting that Ku50 and A4047 may have higher photosynthetic carbon fixation capacity. The net photosynthetic rate of Ku50 was slightly higher than that of A4047 and much higher than that of W14 on the photosynthetic daily variation and Ku50 and A4047 had no obvious midday photoinhibition phenomenon while W14 had, suggesting that Ku50 and A4047 may have higher light conversion efficiency and stronger resistance to high light. The photosynthetic rate curve under different light intensity showed that three varieties of cassava all did not arrive the light saturation point up to the maximum light intensity of 2500 μmol/(m²·s), and the net photosynthetic rate also showed Ku50>A4047>W14. Among them, Ku50 was about 40 μmol/(m²·s), A4047 was about 34 μmol/(m²·s), but W14 was only about 15 μmol/(m²·s). This result was consistent with photosynthetic daily variation and also suggested that Ku50 had stronger resistance to high light and higher light energy conversion efficiency. In addition, the chlorophyll fluorescence parameters were measured to analyze the absorption, distribution and utilization of light energy in different varieties cassava. The result showed that under high light the Y(II) of Ku50 was significantly higher than that of W14, but slightly higher than that of A4047 which had no significant difference (P>0.05). And the NPQ of Ku50 was significantly lower than those of W14 and A4047, indicating that the light energy dissipated into heat on Ku50 was lower than those of W14 and A4047, which in turn proved that the light energy conversion efficiency of Ku50 was higher than those of W14 and A4047, and which was consistent with the results of photosynthetic pigments content and net photosynthetic rate. In conclusion, this research proved that high light efficiency in cassava cultivar Ku50 was induced by high light, and had higher tolerance and utilization rate to high light than wild type of W14 and wild relatives of A4047.