In order to improve the detection efficiency of ring main unit , a release testing system for it was designed according to the function demands. This article discusses the basic functions of the testing system, describes the overall system hardware design ideas and core hardware design process, and introduces a brief description of the software architecture. Combining the hardware and software, a testing system is set up, which can be used for intelligent test of phase-to-phase protection, zero-sequence protection, communication and other functions of ring main unit. After a series of tests, it proves that the system has advantages of less failure rate and high detection veracity rate. The system works effectively.