Considering the factors such as commutation process, residual energy of muzzle and Joule loss of resistance, the equivalent circuit model was established, and the efficiency of conventional helical launcher and a novel helical launcher was analyzed by theoretical, numerical and experimental methods, respectively. The results show that the Joule heat loss is the largest, followed by the magnetic energy loss of commutation, while the muzzle residual magnetic energy loss is minimal. The energy conversion efficiency of the launcher can be effectively improved by reducing the resistance, increasing the mutual inductance gradient, reducing the number of turns in the stator coil unit, and increasing the operating current, etc. However, larger armature coil turns will also bring greater magnetic energy of commutation and muzzle magnetic energy loss, resulting in barrel erosion or even damage, energy release and low efficiency. Besides, the theoretical efficiency of the helical launcher is higher than the one of the railgun under constant current operating mode. The theoretical efficiency of the novel helical launcher is close to 100%, which is expected to be implemented in the case of superconductivity or lower resistance in the future.