With the Green's function tequnique, we have exactly dealed with 3-dimesional lsing model, and obtained the linear equations of the ensemble average of the spin which are able TO be recurrent. Then by applying the decoupling approximation to the spin blocks, we can transform the solution of the transition temperature, magnetization and so on into the solution of algebraic equations. We have shown that for the smaller spin block we can obtain the results with higher precision.