A measurement system was designed to measure the railguns parameters in launching process, which includes Rogowski coil sensor for measuring rails current, B-dot probe for obversing projectiles velocity in bore, net target for catching muzzle velocity, signal condition circuit and high-speed data acquisition card for analyzing and storing data. Its software was also developed in WINDOWS operational environment via modularized design. The designed sensors and test software were successfully used in a practical electromagnetic railgun system to monitor the process of launching. The test results indicate that the state of launching can be intuitively observed and the parameters are accurately acquired and recorded. The software design method can shorten the development cycle, enhance the systems flexibility and provide the interface for the secondary development. The system shows great reliability. It is an effective and practical measurement platform for further research on the electromagnetic launch system.