To explore the response mechanism of diatom to diurnal temperature difference in different environments, Cyclotella meneghiniana was selected to investigate the effects of diurnal temperature difference on its biomass, photosynthetic activity, and nutrient absorption under high and low light conditions. The results showed that in the range of 5 ℃ to 10 ℃, the decrease of diurnal temperature difference can promote the growth of cell density and chlorophyll a and make the specific growth rate increasing. Under high light condition, the maximum quantum yield(F_v/F_m)was significantly different(P<0.05)between groups, and the decrease ranged from 36.3% to 65.2%. But under low light condition, there was no significant difference in F_v/F_m(P>0. 05)between groups. In addition, with the decrease of diurnal temperature difference, the net decrease of PO^3-₄-P concentration in the culture medium increased. The affinity of Cyclotella meneghiniana to silicon varied in different groups. Under high light condition, the affinity of group with 5 ℃ diurnal temperature difference was the highest, and the half saturation constant(K_m)was 1.755 ng/L. However, under low light condition, the affinity of group with constant temperature was the highest, and the K_m was 4.673 ng/L. Under different light conditions, the response of physiological habits of Cyclotella meneghiniana to diurnal temperature difference is different. But in general, the decrease of diurnal temperature difference in a certain range is conducive to the growth and reproduction of Cyclotella meneghiniana.