A machine-maintenance training system was developed on an internet-based multi- user distributed virtual environment where users disassemble and assemble a pump in nuclear power plants. The developed training system has two training modes, i.e., synchronous and asynchronous modes, and it is equipped with the multi-model communication function to provide more effective training environment. The system architecture and the functions of the system for both training modes are described in details, followed by the experimental procedure of the system evaluation. It was confirmed that the users would feel a sense of reality in the training cource by the developed training system.