In order to increase the velocity of the projectile, lots of driving coils are required to accelerate the projectile continuously. Theoretical analysis of e three-stage reluctance coil launcher was made, its working process was simulated by the way of position trigger with the Ansoft software, and the influence of the trigger position on properties of the three-stage reluctance coil launcher was analyzed particularly. The analysis shows that the trigger position has bigger influence on its properties in the design of the three-stage reluctance coil launcher. Each driving coil has the best trigger position to make the projectile exit velocity and energy conversion efficiency is maximum. The research result can be referred by follow-up design and experiment of multi-stage reluctance coil launcher.