A new training environment is proposed for cooperative machine maintenance work in nuclear power plant by utilizing networked virtual environment (NVE) to share virtual reality (VR) environments over network among multiple users and to conduct live communication among remote users. The proposed low cost VR-based training environment consists of (i) 3d virtual rooms with various models of machines and input-output devices in each room and (ii) user interface for communication among users and operation of various machines. A combination of separate server topology and hierarchical server model is employed for simulation of cooperative machine maintenance work through the user interfaces for individual users by a system configuration of 5 PCs connected by local LAN. A simulation experiment were performed for a cooperative machine maintenance training in a virtual nuclear power plant of main control room, cabinet rack room and pump room for calibrating the indications of pump flow meters in the three rooms, and it was confirmed that the constructed prototype was able to provide valid training effects effective to understand how the calibration test should be done cooperatively among the participated members.