The third paragraph of Article 171 of General Provisions of the Civil Law stipulates that the agent who has no right to act as the agent shall be liable for performance of the debts or damages. The liability for substitute performance and the liability for damages are two different kinds of liabilities in nature. The former is contractual liability and the latter is tort liability. The assumption of responsibility for substitute performance actually breaks through the principle of contract relativity and its essence is the general transfer of contractual rights and obligations, that is, the change of contract subject. Based on the particularity of this kind of liability bearing method, in order to prevent this kind of liability bearing from violating the purpose of the agency system itself, it is necessary for the law to restrict the choice of the counterpart in some cases. At the same time, in order to construct a scientific and reasonable system of liability for unauthorized agents, it is necessary for the law to grant the right of negotiation between the unauthorized agent and the counterpart without prejudice to the lawful rights and interests of the principal.