Abstract: In allusion to the phenomenon of repetitive trigger of pulse radar in a certain rocketdrome, the basic principle of radar chain is introduced in this paper. At the same time, the radar raw measure data is analysed when the phenomenon of repetitive trigger appears. By theoretic analysis and demonstration, and experimentation data and display image of radar, the mechanism of the repetitive trigger of pulse radar is analysed when radar works with responder beacon. In the end, the resolvent for the problem is brought forward.