The technical characteristics of government audits make the purchase of social audit services different from the purchase of other public services. Carrying out performance evaluations of outsourced social audit services is important for ensuring effective social audit service outsourcing and for completing comprehensive high-quality audits. On the basis of constructing a conceptual framework for performance evaluations of social audit service purchases under the background of comprehensive audit coverage, the objectives, principles, processes, models, and steps of performance evaluations are clarified. From the perspective of performance evaluation theory, a performance evaluation model and an index system are constructed. On this basis, the evaluation framework is applied to performance evaluations of audit institutions that purchase social audit services. Although outsourcing social audit services solves the problem of coverage quantity relatively economically, there is still room for improvement in terms of efficiency and effectiveness. Audit institutions can continuously improve the performance of outsourced social audit services by building and continuously optimizing the pool of institutions and social audit personnel, constructing a real-time management system for outsourced social audit services, and improving the management incentive system for and performance of outsourced social audit services.