Abstract: So far the wet-adiabatic lapse rate (Γw) was usually taken to be the value of the adiabatic temperature lapse rate(Γa) in cloud. It was based on the assumption that the super-(sub) saturation in condensation (evaporation) process in cloud can be ignored. The expression of Γa is deduced in this paper without such an assumption. It is found that Γa depends on the cloud microstructure and duration of the vertical current with the associated condensation (evaporation) process. In the water cloud Γa≈Γw can be used without significiant error 20s later after the establishment of the current. In ice cloud Γa≈Γw can be used only after 2000s. This result is important for evaluating the static instability in clouds and can be used to explain the fact that turbulence weakens siguificant 1y in the artificially crystalized zone in the stratiform cloud.