In order to study nuclear fission by means of diffusion model we have to solve Fokker-Planck equation. In this paper we present a relevant numerical calculation method of implicit difference. For the nuclear system with viscosity the physical quantities in relation to fission dynamics are calculated, for example, the density distribution, the fission rate, the mean kinetic energy at scission point and diffusion time from saddle point to scission point etc. The results are compared with kramers'stationary analysis solution which is valid for the large viscosity. The comparison and the test of normalized constant indicate that our calculation results are exact.