In this paper we suggest a radiation mobility shift model for the nonuniform channel metal-oxide-semiconductor(MOS). The distribution of two-dimensional(2D)-electric field and 2D-interaction potential, which is caused by the interaction between the ionized impurity in the depletion layer and radiation-induced positive spatial charge, is analyzed by using image charge method. The mobility expression of n-type and p-type nonuniform channel MOS is proposed. Using 2D simulator MEDICI, we simulate the mobility shift with the radiation-induced positive spatial charge. The nonuniform channel MOS's mobility shift numerical results agree well with the analytical results. Uniform channel MOS's mobility shift value agrees with that of the experiment.