In the process of establishing the duty lawyer system, an important system to protect the legal rights and interests of criminal suspects and defendants, the role of duty lawyer has experienced the development process from ambiguity to the person providing legal assistance. Based on the requirements of the United Nations Convention and the concept of defense in modern sense, duty lawyer providing legal assistance should be understood as defense. But duty lawyer is not equal to legal aid defense lawyer. In order to apply duty lawyer system effectively, the consulting right of the duty lawyer should be extended to extract, and duplicate case materials, measures should be taken to increase the financial benefits of duty lawyers and the duty lawyer should be allowed to transfer to a defense lawyer.