Plant design and offline analysis of plant behavior are increasingly being carried out using plant simulators. However, online simulators are rarely used in large plants. The dynamic simulator Visual Modeler developed by Omega Simulation Co., Ltd. is a well-established Operator Training Simulator, and is widely used in training. It also provides similar or higher-speed computation performance than real-time computation in large plants. Using this technology, an online dynamic simulator, which can keep adjusting the parameters of a plant model to correspond with the actual plantpsilas parameters as closely as possible, is called a tracking simulator. We have developed a dynamic data reconciliation technology that enables the dynamic simulator to adjust the parameters of a plant model to the actual plantpsilas parameters even when plant behavior is not steady. This technology will facilitate early fault detection in processes and prediction of future plant behavior, thereby assisting innovation of plant operations.