Abstract: Based on circuit theory, an electrical mathematical model of multi-level induction coil gun is established. The influencing factor of armature force is analyzed. The results indicate that the armature force is determined by the drive coil and the armature current and the mutual inductance gradient. Principle of designing multi-level induction coil gun is presented. According to the principle, the optimum launch control strategy of induction coil gun is presented, and is approved practicable by theory. At last, taking ten level induction coilgun as an example, trigger formula of multi-level induction coilgun is presented, and experiments are done to verify the calculation method. Amending the trigger formula, the simulation results agree well with the experimental results.