A novel physical model for the process of silicon anisotropic wet chemical etching is proposed. Based on the actual process of chemical etching reaction, a series of microscopic parameters describing the process have been put forward and non-linear equations with a removal probability function have been listed. For the transfer probability function in the equations, not only have the removal probabilities corresponding to the different microscopic states been included, but also the influence of etching temperature and etchant concentration. Moreover, the influences of the first neighbourhood atom and second neighbourhood atoms on etch rate are all included in the transfer probability. Having compared the calculated results against the experimental data, the feasibility of the model has been demonstrated.