The diurnal variation of the tropical convection is investigated using hourly outputs from a two-dimensional cloud-resolving model simulation. The features of cloud microphysics in tropical convections are proposed by the contrastive analysis of the simulation. The model is forced by the observational data obtained from tropical ocean global atmosphere coupled ocean-atmosphere response experiment as the initial and boundary fields. The diurnal composites are carried out in weak diurnal SST variations （case W） and strong diurnal SST signals （case S） according to the amplitude of diurnal SST variations. The simulation results show that the ice water path in case W is larger than the liquid water path in case S, and more water cloud and less ice cloud exist in case W than in case S. The results also show that the surface rain rates reach their peaks in the early afternoon in case S, while the surface rain rates reach their peaks in the night in case W. Further comparison of cloud microphysics budgets shows that the coagulation of precipitation ice （sum of snow and graupel） is less than the coagulation of liquid water （sum of cloud water and precipitation water） and ice cloud can be formed in case W.