Abstract: The third-party evaluation can meet the requirements of the principal, whose evaluation procedures are legal and normative, and the evaluation can play a regulatory role. The principal's risk-avoidance principle makes it attach great importance to capital supervision, therefore the evaluation positioning is unclear, making the evaluation a regulatory tool. Based on the response needs and cost-oriented logic, the assessors choose to focus on “trace management” and fund supervision, but pay little attention to effect evaluation. Government purchasers are not “smart buyers” and social organization contractors are not mature service providers, which are the main sources of “unprofessional” third-party evaluations. Grassroots local governments and social organizations tend to “co-conspire”, which makes the evaluation show a situation that is scientific in form but cannot be strictly enforced in practice. The problems in the implementation of the third-party evaluation can be solved by improving the access standard of the evaluation party, training the buyer to become a smart buyer, and supervising the receiver to become a qualified service providers.

Key words: principal-agent, social service project, third-party evaluation