In order to understand the effects of temperature, light, phosphate and their interactions on the growth and chlorophyll fluorescence characteristics of Skeletonema costatum, each environmental factor was set at three levels[Temperature:17,23,29℃; Illumination:80,120,160 μmol photons/(m²·s); Phosphate:0.1,1,10 μmol/L]. Using L18 (3⁷) orthogonal experimental table and considering interactions between two environmental factors. The changes of the chlorophyll a concentration and photosynthetic activity of Skeletonema costatum were studied by indoor culture experiments. The results showed the chlorophyll a peak value of Skeletonema costatum could reach a higher level at 10 μmol/L phosphate concentration. The optimum combination of environmental factors was 23℃, 120 μmol photons/(m²·s) and 10 μmol/L. Phosphate had a significant effect on the chlorophyll a peak value of Skeletonema costatum (P<0.01). Temperature, light and the interaction between environment factors had no significant effect on chlorophyll a peak value (P>0.05). It was found that Skeletonema costatum had higher photosynthetic activity at 10 μmol/L phosphate concentration. But the photosynthetic efficiency α showed no significant difference with phosphate concentration. Light significantly affected the maximum quantum yield F_v/F_m (P<0.05) at 10 μmol/L and 1 μmol/L phosphate concentrations:The F_v/F_m of Skeletonema costatum was higher at 80 and 120 μmol photons/(m²·s) while the phosphate concentration was 10 μmol/L. The F_v/F_m was lower at 120 μmol photons/(m²·s) while the phosphate concentration was 1 μmol/L.