Abstract: The derivation and simulation of two-sphere model coupling with multiPle diffusion mechanisms have been conducted under the condition of volume conservation. The neck growth equation and shrinkage for copper have been computed with different sintering time, temperature and particle size. The neck equation given by the coupling model is greater than that given by surface diffusion modal. The shrinkage given by coupling model is less than that given by the model only considering grain boundary diffusion and volume diffusion. The simulation indicated that time index of neck growth equation becomes lower with the increase of sintering time. The contribution to neck growth from each mechanism has been given under different conditions. The Paper indicated that slow heating rate gives more shrinkage and bigger initial contact radius gives less shrinkage