The attention on the streaming media applications based on RTSP protocol is growing, so the main issue we address in this paper is how to evaluate the serving performance of RTSP streaming media server. With comprehensive analysis of the performance metrics of streaming applications, we propose an approach to design and implement a Performance Testing Tool for RTSP-based Streaming Server. The tool creates the testing environment by obtaining parameters from the script of test case, utilizes multi-thread mechanism to create multiple pseudo-terminal instances to simulate a certain number of concurrent users for sending RTSP signals, receives media flow, analyzes RTP packets without decoding, and calculates the related performance metric values of the server finally. Experiments validate the efficiency and accuracy of the tool.