A computer simulation software named EVSIML has been developed and is being brought to perfection all along. It has combined the MATLAB and Visual C++ programming languages and the Object-Oriented programming technology. The software of EVSIML (Electric Vehicle SIMuLator) is developed by MATALB and Visual C++ (VC) programming languages with Object-Oriented technology on the basis of the drivetrain model of the EV. It makes features of programming of MATALB and Visual C++ with Object-Oriented technology. EVSIML is mainly used to simulate the power performances and fuel economics of EV originally and now its functions have been expanded in order to deal with much computation and analysis about engineering including system match and control analysis. At the same time, as a complicated simulation software, excellent Graphical User Interfaces (GUI), high efficiency, quickly execute speed, good reusability, good maintainability and good expandability are also absolutely necessary. The paper will present the latest improvement on EVSIML and the new features of it in detail. In order to maintain the energy security of China, improve the air quality and enhance the competition of automobile industry of China in the world, the national science ministry of China has especially founded the special important EV project in the national tenth-five and 863 program, plan to emphasize particularly on the industrialization of the EV, exert to gain a significant breakthrough in the key cell technology, the system integration technology and the whole vehicle technology of the EV. The EV is a complex system that integrates a number of subsystems such as the vehicle body, electric propulsion, and energy source and energy management. The technologies involved are diversified and multidisciplinary, including electrical and electronic engineering, mechanical and automotive engineering, and chemical engineering. Because of these multidisciplinary and fast-changing EV technologies, the design process of the EV should be flexible, prompt and economical. Computer simulation not only facilitates this design process, but also enhances the system optimisation of the EV.