In terms of the social exchange theory, social comparison theory and the fulfillment of employee's justice and voice, this paper discusses the relationship between the psychological contract fulfillment and job involvement of dispatching workers, as well as the mediating role of distributive justice and procedural justice and the moderating role of union member. Based on samples of 171 dispatching workers from 7 leasing agencies in South China by questionnaire, the results of the analysis made by the structural equation model show that psychological contract fulfillment is positively related with job involvement; while distributive justice and procedural justice fully mediate the psychological contract fulfillment-job involvement relationship. The results of the analysis made by the hierarchical regression equation also reveal that union membership moderates the relationship between procedural justice and job involvement that is to say, for dispatching workers who are union member, this relationship is stronger, but for those who are not union member, weaker. In the final section, significance and implications of these results are discussed.