Abstract: Based on the process role theory form a professional identity cycle model, the formation mechanism of clinical professional identity of undergraduate nursing students is explored in the three stages of role expectation, role understanding and role practice, to explore the obstacles and promoting factors in the formation process of professional identity and the final professional identity results. In the results of this study, occupational solidification, occupational value and occupational support are the hindering factors for the professional identity of nursing students. The promoting factors include self-expectation, others' recognition and clinical adaptability, and form two kinds of professional identity results of participants and bystanders in the final. The formation process of professional identity reflects the transformation process of nursing profession modernization, the game process between traditional social structure and modern individual consciousness. Although undergraduate nursing students have a professional identity dilemma in the role expectation and role understanding, most undergraduate nursing students still show a positive role practice attitude, forming a spiral pattern of professional identity.