Abstract: An uninterruptible power system (UPS) testing method includes the steps of setting an operational decline table, setting an initial value, collecting data, inputting targets, executing multi-algorithm, and indicating a warning or an approval. Wherein, battery cells of the UPS are repeatedly tested when being actually used at different temperatures to set the operational decline table and the initial time value; and data about temperatures and time periods of the battery in operation are continuously collected for a user to execute algorithms based on designated conditions to predict the battery state in a future time period; and an indication message is generated for the user to determine whether the battery is still usable or has to be replaced. In this manner, it is able to estimate the running time of a target time of the UPS without the need of performing an actual electrical discharge procedure.