Based on the SIRS model with the direct immunization on complex network, an improved SIRS epidemic model is proposed in this paper. The proposed model is built by considering the case that infective individuals enter into the removed or susceptible state when they are cured. By using the mean-field theory, an epidemic threshold of the model is obtained focusing on the improved model. The simulated results illustrate the valid of the theory analysis. Both the theoretical analytical and simulated results indicate that whether the disease becomes the endemic disease or not is influenced by the proportion from the infective state to the susceptible state.