Existing virtual assembly systems are lacking in sense of reality. This paper explored a new assembly simulation system based on virtual reality technology to enhance immersion. After comparison of available technologies, the new system was built with Unity3D as the virtual reality simulating platform, virtual reality helmet as the virtual assembly displayer, Leap Motion as the interactive device, and corresponding algorithms to assist gesture recognition and collision detection. The new system enriches the interaction between the operator and the device, reflects the assembly process more real and increases the efficiency of actual assembly problems solving.