Due to the complexity inside the drop after impact on solid surfaces and the interaction among gas, liquid and solid phases, it is difficult to investigate the shape variation of the drop through the theoretical analysis, and most studies have focused on experiments and numerical simulations. In this paper, expressions for empirical coefficients of inertia, viscosity and surface tension are acquired by analyzing the force state. The drop oscillation model after impact is built further. The expression of the drop spreading radius, and the effects of surface tension and viscosity on the spreading process are obtained. Finally, the correction factor in the drop oscillation model is determined and the feasibility of the model is verified by comparing the computational results with the numerical results.