Aiming at the problems of long design cycle, the inability of real-time dynamic display of design effects and the non-cross-platform linkage of design products in the design process of rail vehicles, a virtual design system for rail vehicles based on Unity3D virtual engine is proposed. Based on this virtual design system, the whole process of virtual design from the overall design, key component structure design, virtual disassembly and assembly to virtual running test is developed and realized. Fan-shaped collision inspection and AABB enclosing detection method based on mountain climbing method are used to realize high-efficiency and high-precision human-computer interaction; the model instantiation technology is applied to reduce the amount of system models and achieve lightweight design; Ansys is used to realize Unity3D and Ansys Platform linkage. The results show that the system realizes the low-cost, high-efficiency, multi-style design process of rail vehicles, and provides a reference direction for the design and application of virtual reality technology.