OTS (Operator Training System) is becoming popular for the safe and effective operation of chemical processes and control systems. This paper outlines the total hardware system superstructure and software modules of yOTS (Yonsei Operator Training System) which we developed. yOTS is a network based multi-training system composed of a workstation-based server module and PC-based user modules. The user module has a DCS-like user interface and sends data to OM (yOTS Manager) over the network. Reliability and stability are essential for the successful development of distributed OTS. State-of-the-art technologies of efficiency and stability are mainly considered in this paper. yOTS is superior to other OTS in its ease of handling discrete events, managing process models, expanding module functionality and multi-training over the network. The structure of yOTS and core algorithm for a multiple trainer over the network is also presented. A batch process example is used to illustrate the proposed advantages of yOTS.