This paper focuses on the grass-roots civil servants and aims at identifying the influence mechanism of benevolent leadership on their service performance and the role of psychological capital among the triadic relationship. The result of hierarchy regression analysis about 350 sample data showed that both benevolent leadership and psychological capital had significantly positive effect on grass-roots civil servant's service performance, while psychological capital acted as a moderator between benevolent leadership and grass-roots civil servant's service performance. Therefore, it is highly recommended that public organizations should pay attention to the individual's spiritual need, create a caring atmosphere so as to improve the service performance of grass-roots civil servants, increase the administrative efficiency and further promote the harmonious society