The professionalism of social work can be divided into two types: professional support type and identity transformation type. The social identity of social work occupation includes the internal and external recognition of professional groups. Focusing on the professional identity within the group of professional support, based on the perspective of social support theory, this paper explores the factors influencing the professional identity of social workers. The results show that social support at the micro level (family support) and the middle level(organizational support) are important to social workers, and have no significant impact at the macro (institutional) level. Therefore, suggestions are put forward such as increasing the investment in staff training and supervision in institutional management and social work service projects, increasing the publicity of social work specialty to the public, and formulating relevant policies.