Electromagnetic coil launcher is a kind of special linear motor. In order to study the trigger principles of multi‐stage electromagnetic coil launcher, based on the electromagnetic field theory, the paper deduced the field‐circuit coupling magnetic field control equations of multi‐stage synchronous inductive coil with the consideration of inter‐stage coupling, and analyzed the distribution law of magnetic lines of force, air‐gap magnetic field and current density for multi‐stage electromagnetic coil launcher. The following conclusions were reached: the largest part of magnetic flux was at the intermediate stages of multi‐stage electromagnetic coil launcher; each stage of drive coil compensates for the magnetic field of the upper coil, thus making a stable air‐gap magnetic field; the induced current density was mainly distributed in the tail and surface of the armature; according to anti‐electromagnetic shock design principle of multi‐stage electromagnetic coil launcher (namely, the requirement for small fluctuation of electromagnetic force), the basic principle of multistage trigger was summarized, that is the principle of keeping air‐gap magnetic field and induced current constant. Thus, the design foundation was laid for the operation of multistage electromagnetic coil launcher. © 2021 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.