This paper deals the numerical analysis on mass transfer under forced convection cooling. The transients of frost profiles on a cooling plat in a narrow channel were calculated by use of the packaged software with built in some original subroutines. In this paper, the architecture of these subroutines and this benchmark tests were showed. The calculation results exhibit local mass transfer rates and clarified following things. On the leading edge of the cooling plate, the frost accumulation accelerates locally. For the prediction on the cooling plate temperature distribution, to take into account latent heat of sublimation is necessary. In addition, the comparison between calculation and experimental results shows below issues. Both frost distribution profiles overlap in upstream; on the contrary, they do not overlap in the downstream. This comparison result indicates that the super saturation or mist flow is not negligible in the downstream. In terms of total frost weight, both results are roughly agreed and this weight increases proportionally with a run time despite increasing of the heat resistance caused by frost layer.