This paper explores the social media's impact to the internal process of local government from a theoretical perspective of informal organization.Based on the WeChat datum from civil servants of city Z，this paper finds out that：WeChat group has become a prevailing way of informal organization generating within local governments in which civil servants can duplicate actual organization structures and team up members for task assignments.WeChat groups duplicating actual organizations improve job involvement and provide emotional supports.WeChat groups that team up task participants facilitate coordination among departments，reduce uncertainties and ambiguities of task objectives，clarify implementation standards，redistribute job duties and responsibilities and foster consensus within group members.The use of WeChat group demonstrates the mechanisms of self seek order building from individual organization members which reflects，at the micro level，how social media technology shapes and reinvents the structures and processes of the hierarchy in public organizations.