Abstract: In order to make the reasonable and effective technical schemes for overhauling and solve difficulties in training overhauling workers in hydroelectric power plants, a computer simulation system for overhauling of a hydroelectric generating unit was developed by combining computer-aided simulation, virtual reality and multimedia techniques. The key techniques in this system include 3-dimensional digital modeling for all the parts of a hydroelectric generating unit, knowledge database setting up for overhauling technique and precess, implementation of 3-dimesnsional visualization, and dynamic simulation of assembling processes based on the virtual reality and multimedia techniques. This system has been successfully used in the overhauling of a large hydroelectric generating unit and the training of overhauling workers.