In order to strengthen a sense of belonging and cohesion, China trade union has dedicated to resolving the "Sihua" issue through a series of measures, such as improving rights-protecting function, modifying organizational structure and holding union events, which become theoretical common ground and yet require further verification practically. On the basis of survey on 2457 employees from 142 companies, this study lays emphasis on the positive correlation between employees' cognition towards union and union cohesion under Chinese circumstances, with the guidance of social exchange theory. Research results are as followed. During the union reform process, employees' cognition towards union's rightsprotecting function (perceived union instrument) does consolidate their sense of belonging and identity to union (union commitment); besides, union activities promote a sense of cohesion through enhancing union participation. In the meantime, the redundancy of managerial hierarchy and the poor communication between superior and subordinate (power distance) can inversely stimulate employees' enthusiasm to union community -- longing for union's endorsement, further leading to reinforcement of union attraction, cohesion and competitiveness. In the end, the study offers suggestions on union construction and organizational management.