The t_J model is one of the most important models that is often used to stud y the theory of the effect of strong electron correlations and high_Tc superconductivity. In this article, the method of renormalization group is use d to investigate the t_J model， and the elementary excitation energy spectra of t_J model (Ｔ≠０) are obtained by the flow equations. The result is compared with that of Green's function method and agrees with its result. At th e same time, the result of renormalization group method is the analytical soluti on while that of Green’s function method is the numerical solution.