Vitis davidii Foёx. was used as material, four treatments of potassium(0, 135, 270 and 540 g/plant) were designed to study the influence of potash fertilizer on photosynthesis. Results showed that higher net photosynthetic rates were achieved at the treatment of 270 g/plant, maximum appeared in veraison period，which was 8.91 μmol/(m2?s); stomatal conductances were higher at the treatment of 540 g/plant in every period; highest transpiration rate was got in expand period at the treatment of 270 g/plant, it was 5.33 mmol/(m2?s); the intercellular CO2 concentrations of 270 g/plant were lower than other treatment except in bloom period. There were extremely significant positive correlations between potassium and net photosynthetic rate, transpiration rate and stomatal conductance; the photosynthetic diurnal variation presented a bimodal curve in different periods, showing the peak at 10:00 and 16:00. The treatment of 540 g/plant had the highest net photosynthetic rate at expand (6.05 μmol/m2?s), veraison (7.63 μmol/m2?s) and defoliation period (4.75 μmol/m2?s) at 10:00, respectively. The treatment of 270 g/plant came second, while the treatment of 135 g/plant and 270 g/plant had the highest at bloom period(5.31 μmol/m2?s) and at mature period (5.61 μmol/m2?s), respectively. At 16:00, except the treatment of 540 g/plant had the highest net photosynthetic rate at bloom period, the treatment of 270 g/plant had the highest net photosynthetic rates at expand, expand, veraison, mature and defoliation period, which were 4.26, 3.61, 2.87 and 2.30 μmol/(m2?s), respectively. In conclusion, the application of 270 g/plant potassium is benefit for photosynthesis of Vitisdavidii Foёx.