Abstract: Taking 4 cultivars of Viola tricolor, i.e., 229-18, EP1, ZMY2-1 and 08-H2 as study objects, the characteristics of photosynthetic physiology and ecology of the plants during florescence stage and the relevant influencing factors were studied with Li-6400 portable photosynthesis tester in north of Henan Province in May. The results showed that the diurnal variation of net photosynthesis rate of V. tricolor leaves showed two peak curves in May, the highest peak occurred at 10:00 am, indicating a ‘nap’ phenomenon. The light saturation caused by strong sunshine and the followed high temperature at noon time were the important ecological factors leading to the photosynthetic ‘nap’ of V. tricolor plants. There were significant correlations among the relevant ecological factors. The major physiological factors that affected the diurnal Pn variation were transpiration rate (Tr) and photosynthetic available radiation (PAR), there was a significant positive correlation between Tr and PAR. The cultivar 08-H2 showed higher level of light saturation point (LSP) and photosynthetic quantum efficiencies, whose Pn, Tr and sunlight use efficiency(SUE) were all significantly higher than those of other cultivars, indicating that this cultivar had higher photosynthetic capability and waterdemand characteristics.