This paper focuses on the numerical simulation of non-equal sintering metal powers by surface diffusion. In order to simulate the sintering process of non-equal metal powders clearly, the surface diffusion model is modified by establishing more suitable initial boundary conditions. And this model is numerically solved by the finite difference method. The three-dimensional numerical simulations of two metal powers with radii ratios 1:1, 1:1.5, 1:2 are implemented by this model. Through comparison, the simulation results are consistent with the experimental ones. Finally, the effect of metal powders’ radii ratios on the growth rate of sintering neck is investigated, which implies that the sintering neck radius increases with the decreasing of radii ratios.