Abstract: Synchronizing trigger is a difficult problem which is eager to be solved during the research of multistage coil launcher. Based on the analysis of optimal trigger position characteristics, trigger strategy was proposed so that the optimal trigger position can be determined by initial velocity of armature. Relationship between armature velocity and optimal trigger position was obtained by simulation. Synchronization trigger was realized for the coil launcher at arbitrary armature velocity by the combination of real-time velocity measurement and time-delay program. The armature velocity measurement circuit is designed based on the photoelectric sensor, high voltage trigger pulse generating circuit, control circuit and the software flowchart. The reliability and compatibility of the system is verified by experimental results.