Electromagnetic rail launcher(EMRL) will enjoy a promising future in the military application because it has many advantages compared with conventional weapons, such as high muzzle velocity, energy sources facility, easily controlling, excellent work capability etc. One of the main problems of electromagnetic rail launcher is the heating to melt in some special places of the rail and armature, and the rail launcher will be disabled. In this paper, the working principle of the EMRL is analyzed. With finite element analysis code the simulation model of the EMRL is set up and electromagnetic-thermal coupled analysis of the EMRL is accomplished. The laws of current distribution, EM force distribution and temperature distribution of the armature vs. time are achieved. The varying laws of EM force and temperature in armature resulting from its loads changing are also analyzed. All of these results will provide guidance for the following engineering project.