In this paper, we study the service importance evaluation problem in the smart grid. Considering the complexity of power communication services is gradually deepening with the accelerated intelligent process of modern power grid, we propose an evaluation method combining multiple factors fusion aimed at improving the accuracy of evaluation results and reflecting the real status of services in the smart grid. In the proposed method, we first establish a comprehensive evaluation model that contains the complete evaluation indicator system for two factors and introduce the concept of contribution coefficient. Then we propose the evaluation method for single factor and quantify the evaluation indicators of service importance based on communication factor and power grid factor respectively. According to the multi-factorial characteristics of services, the fusion process of two-factor service importance is carried out by contribution coefficient finally. Case analysis shows proposed approach can overcome the disadvantage that traditional methods only apply to single factor or fail to effectively combine expert's subjective judgment and the objectivity of evaluation methods, meanwhile guarantee the rationality of evaluation results.