In order to improve the launching efficiency, the force of armature with large weight in single-stage coil launcher is analyzed. Based on the motion law of large weight armature in coil, a single-stage coil launching model is established by using simulation software. The motion characteristics of armature with different weights and the force of armature entering coil at different initial speeds are simulated and summarized. The efficiency of the 2 cases is compared. The results show that under the same discharge circuit parameters, the armature mass increases, the reverse time of electromagnetic force delays, the initial speed of armature entering the coil increases, and the reverse time of electromagnetic force advances. The launching efficiency can be improved by adding the model of bomb-ray circle.