Reluctance driver is a new type of linear electromotor. According to the electromagnetic force between the current in driving coil and the magnetic current in projectile, the projectile would be accelerated to a scheduled velocity. In this paper, the theory model and its calculation methods has been introduced. Once the structure of the driving coil and projectile parameters have been given, the equivalent inductance between driving coil and projectile has became the non-linear function of the current in the driving coil and the projectile's position. The equivalent inductance date has been acquired according to the finite element software. According to the voltage and power balance equations of the electromechanical system and the equivalent inductance date, the variable parameters of the launch process such as the voltage on the capacitor and the muzzle velocity of projectile have been numerical calculated. The ferromagnetic projectile has been used for the experiment and the muzzle velocity of experiment is mainly the same as the result from numerical calculation.