ISP network performance evaluation is very important to the improvement of application performance, the optimum competition of ISP network and the operation and management of Internet. ISP network consists of one or several autonomous systems (AS), so AS is chosen as a basic unit of performance evaluation. The performance measurement architecture of AS was put forward, and performance matrix model of AS was constructed. A method of AS performance evaluation was put forward based on AS performance matrix model. The evaluation method adopted weighted average of path performance between border routers as comprehensive performance metric of AS. Simulation results indicate that the method can evaluate AS performance effectively.