To ensure the safe operation of offshore plants, a system is needed for evaluating the equipment performance and for monitoring the results. Currently, owing to the operating environments of of shore plants situated far from the land, measurement data must be periodically stored in storage devices and carried on the land for evaluating the equipment performance. Consequently, it is difficult to prevent equipment failure because the performance evaluation cycle is long. Furthermore, until the next performance evaluation is conducted, it is difficult to determine the equipment's degree of performance degradation. Hence, it is necessary to install an onboard equipment performance monitoring system within the offshore plant. In this study, to evaluate and visualize the results of equipment performance within an offshore plant, a database was designed as the initial step towards the development of an equipment performance monitoring system. The tag data of major equipment were selected and analyzed. Furthermore, in order to store and manage the data measured in real time within the offshore plant, a database was developed for the onboard equipment performance monitoring system.