Based on the governing equation and the associated boundary conditions, the analysis solutions for the condensation are obtained, and the effect mechanism and main factors of mass transfer and interface on the condensate are discussed, such as the factor B expressing interfacial velocity effect, the factor characterizing effect of mass transfer, and the factor w denoting comprehensive effet of mass tranfer and interface on the condensation.The calculation ressults show that mass transfer and interface have obvious influence on the condensation. The present study differs from that of the Nusselt's theory.