Abstract: In order to clarify the diurnal variation of high and low starch cassava leaf photosynthesis and starch accumulation, diurnal changes of photosynthesis, soluble sugar contents and starch accumulation and the difference of stomatal density in leaf abaxial / adaxial epidermis were studied, of which high and low starch cultivars was used as materials. The results showed that, the photosynthetic rate of high starch cultivar ‘Fuxuan01’ was higher by increasing illumination intensity compared to that of low starch cultivar ‘Huanan124’, and stomatal density of the leaf abaxial / adaxial epidermis was significantly higher for ‘Fuxuan01’ than that of ‘Huanan124’. For two cassava cultivars, the sugar and soluble sugar contents of leaf was progressively increased from 8:00 to 18:00, and the leaf starch contents accumulated the highest at 18:00 in a day. However, there was significant difference in photosynthetic ability between the high starch cultivar ‘Fuxuan01’ and low starch cultivar ‘Huanan124’, and the photosynthetic ability and accumulating sugar contents for ‘Fuxuan01’ was higher from 8:00 to 14:00, and then ‘Huanan124’ was higher from 16:00 to 18:00. This difference was related to higher gas temperature, which resulted in higher leaf temperature, decreasing the activity of chloroplast and Rubisico and RuBP regenation ability. This was accorded with higher temperature resistant of ‘Huanan124’.