Abstract: In order to investigate the effects of diurnal temperature difference on the growth of Phaeodactylum tricornutum and Heterosigma akashiwo, we cultured these two species batch and semi-continuously at three temperature levels (18℃: 18℃ for both light and dark period; 22℃: 22℃ for both light and dark period; 22—18℃: 22℃ for the light period and 18℃ for the dark period). The results showed that: (1) Compared with 18℃, 22—18℃ reduced the cell density of P. tricornutum during batch culture at the plateau phase, but did not affect the latency time. In the semi-continuous culture, 18℃ had the highest specific growth rate (µ); for H. akashiwo, temperature had no significant effect on the cell concentration in the plateau stage, but 18℃ and 22—18℃ had prolonged latency time compared with 22℃, and 22—18℃ significantly decreased the growth rate; (2) In batch cultivation, the chlorophyll a (Chl.a) and carotenoids (Car.) content of P. tricornutum and H. akashiwo decreased significantly in 18℃ compared those in 22℃. Under semi-continuous culture, the temperature did not affect the Chl. a content, but 22—18℃ increased the Car. content of H. akashiwo by 24.5% compared to 22℃ treatment; (3) Temperature had no significant effects on the maximum effective photochemical efficiency (F_v/F_m) of photosystem II in P. tricornutum and H. akashiwo under both batch or semi-continuous culture; In batch cultivation, 18℃ showed higher effective photochemical efficiency (Ф_PSⅡ) and photochemical fluorescence quenching (Qp) under 600 µmol/(m²·s) conditions than other 2 conditions; (4) Both P. tricornutum and H. akashiwo showed higher carbon fixation rates at 22—18℃. Thus, this study provides a new perspective to explore the influence of temperature changes on the structure of phytoplankton community.