With the further research on electromagnetic rail launch technology, one of the important research aspects of electromagnetic railgun is to improve launch efficiency. The improvement of launch efficiency means an increase in the cost-effectiveness ratio of the system and a smaller scale of system volume, weight, and cost. Therefore, it is important for the engineering application of electromagnetic launch technology. This article proposes a method to increase the magnetic induction intensity in the inner barrel by adding a high permeability magnetic medium layer on the outer side of the barrel, which can enhance the launch capability of electromagnetic railgun effectively. The relationship between the thickness of the magnetic medium layer and magnetic induction intensity in the inner barrel was discussed and an optimal thickness was obtained. A typical example shows the effect of adding an appropriate thickness of the magnetic medium layer on improving the launch efficiency of the system. The results show that the effect of magnetic medium enhancement can not only increase the launch efficiency, but also improve the service life of launch system.