Electromagnetic rail launch technology is an electrical launch method that converts electrical energy into armature kinetic energy. It has widespread applications in both military and civilian fields. It can accelerate the armature to several kilometers per second within milliseconds, offering advantages of high speed, fast response, and controllable velocity compared to other launch methods. In order to meet the requirements of ultra high speed experiments and load delivery applications, this paper develops a small-caliber electromagnetic rail launch system. We designed an electromagnetic rail launcher model, and the system components include a pulsed power supply system, electromagnetic rail launcher, armature, etc. A multi-physics coupling simulation model covering electromagnetic fields and structural mechanics was established. The simulation results reveal key physical laws such as current curves, electromagnetic fields, and structural stress-strain within microseconds. This study demonstrates that the designed small-caliber electromagnetic rail launch system has reliable structure and meets the launch performance indicators. This research not only provides critical technical pathways and theoretical basis for the engineering implementation of small-caliber electromagnetic rail launch systems but also the constructed simulation platform has significant reference value for the design optimization of similar systems.