In this paper, the optimization for blade photosynthesis and culture conditions at different light intensity and temperature in Ulva linza with pulse amplitude modulation chlorophyll fluorometer (PHYTO-PAM). The results showed that F_v/F_m, F_m, F_v and α value were the highest at 25 ℃ temperature and 72 μmol/(m²·s) light intensity, up to 0.74, 4567, 3406 and 0.305 respectively. When temperature and light intensity were lower than the point, light unsaturation would occur. And the farther the temperature and light intensity was from the point, the greater their F_v/F_m, F_m, F_v and α value decreased (P<0.01). At 5 ℃ and 35 ℃ with 72 μmol/(m²·s) light intensity, the F_v/F_m, F_m, F_v and α values were the lowest, about 32.24%-64.88% and 22.99%-53.44% of that at 25 ℃ with 72 μmol/(m²·s) light intensity, respectively. And at 18 μmol/(m²·s) and 216 μmol/(m²·s) light intensity with 25 ℃, the F_v/F_m, F_m, F_v and α values also were lowest, which were 44.94%-82.62% and 51.82%-76.72% of that at 72 μmol/(m²·s) light intensity with 25 ℃, respectively. F₀ did not change much. At 5-30 ℃, F₀ first increased and then decreased or increased again, while at 35 ℃, it firstly declined and then increased. As for fitting parameter α, it was showed that Ulva linza enhanced photosynthesis by increasing light energy absorption before light saturation point, but after that, they would increase photosynthesis by rapid declining light energy absorption. rETRmax Duncan test showed that the high / low temperature and high light intensity inhibited photosynthesis rate significantly (P<0.01). It indicated that the temperature between 15 ℃ and 25 ℃ and light intensity between 54 μmol/(m²·s) and 72 μmol/(m²·s) were feasible photosynthesis and growth conditions for Ulva linza, and too high or too low were not good. The temperature order for photosynthesis and growth rate was 25> 20> 15> 30> 10> 5> 35 ℃, and the light intensity order was 72>54/108>36/162>18/216 μmol/(m²·s).