The Pn-PAR response curve and diurnal variation of photosynthesis of a new tea cultivar Guilyu-I were measured and analyzed with the Li-6400 portable photosythesis measuring system. The results showed that the curve of diurnal variation of net photosynthetic rate (Pn) could be described as unimodal curve, and the peak value was 9.36βμmol·m^-2·s^-1, which occurred at 11:00AM. The curve of diurnal variation of transpiration rate was also showed in a single peak curve, but the peak value appeared at 15:00, which was 4.06βmmol·m^-2·s^-1. The stepwise multi-regression analysis showed that the photosynthetically active radiation and air relative humidity were the main direct factors which affected the diurnal variation of Pn. The light compensation point and light saturation point in cultivar Guilyu-I were 7.13 and 354.60βμmol·m^-2·s^-1 respectively. And the apparent quantum yield was 0.088 mol·mol^-1. This study provided a theoretical basis for fast-growing and high-yield cultivation, and for the establishment of cultivation management strategy of the introduction of Guilyu-I cultivar.