Based on characteristics that different layers of skin mainly consist of cells and liquid between cells,a feasible three-layer physical model,which had used methods of porous medium,was put forward. Mathematic equations about conversation of consistency and energy were founded according to peculiarities of different layers. Analytical solutions were given by using the equations of consistency. On the condition of different blood flow rate, coefficients of mass transfer and thickness of layers,the changes of consistency were calculated by programming. These results are consistent with the results coming from experiment of mass transfer coefficients.