Abstract: Collaboration among public organizations, private organizations and individuals increasingly becomes one of the key points and difficulties in public management. This paper studies the trans-department collaboration in public fields in perspective of knowledge collaboration. It descriptively anlyzes the status quo of knowledge collaboration in handling public affairs with empirical methods. It describes the frequencies of knowledge collaboration among different collaboration bodies and different collaboration patterns. It is found that the motives of knowledge collaboration in turn are: improving the efficiency and quality of public service, bettering the policy making and solving the social problems more intelligently. The main obstacle hindering knowledge collaboration within public sectors is lacking of information exchange platform while the main obstacle impeding trans-organizational knowledge collaboration is the conflicts of interests. The consideration of self-interets comes first when organizations decide whether to attend the knowledge collaboration.