Abstract: The features of diurnal variation of sea surface temperature (SST) are simulated in the LASG/IAP Climate System Ocean Model (LICOM) by resolving the diurnal variation of solar radiation and the influence of weak mixing is investigated. Forced by the ideal diurnal variation of solar radiation, some features of diurnal variation of SST can be captured in LICOM with 10-m vertical resolution in the upper layers. The diurnal variation of solar radiation also results in diurnal variation of currents in the upper layers. The horizontal distribution of diurnal amplitude of simulated SST is consistent with that of observed SST and modulated by the diurnal amplitude of solar radiation. In the eastern Pacific cold tongue, the diurnal amplitude of simulated SST is about 0.3℃－0.4℃ and 0.1℃－0.2℃, smaller than that of observations. The peak of daily SST variation appears during 1500－1600 LST and lags 2－3 hours than the peak time of daily solar radiation, which is close to observation. After reducing mixing, the diurnal amplitude of SST variation increases in the equatorial eastern Pacific cold tongue, closer to observation. This indicates that the features of diurnal variation in the equatorial eastern Pacific cold tongue are mainly controlled by the diurnal variation of solar radiation and vertical mixing. After reducing mixing, under the modulation of solar radiation, the mean states including the mixed layer depth, temperatures and currents are obviously changed. In the northern part of the eastern Pacific cold tongue, the reduced mixing causes heat accumulation in the upper layers and then leads to an increase in SST about 0.3℃. While in the southern part, the enhanced meridional advection leads to a decrease in SST about 0.2℃.