The t-J model is one of the most important models that is often used to study the theory of the effect of strong electron correlations and high-Tc superconductivity. In this article, the method of renormalization group is used to investigate the t-J model and the elementary excitation energy spectrum of the t-J model is obtained by using the flow equations. Using the symmetry of functions, we can solve the specific expression of the energy spectrum. The result is compared with the result of Green's function method.