Battery performance test uses DC discharge test method commonly. The DC discharge test load used in this method has certain requirements for the battery configurations, so it lacks versatility. This paper presents a battery performance test method of UPS based on AC discharge by utilizing the characteristics of UPS to output AC power. The principle of this method is analyzed in detail and experiments are carried out. This method can be applied to UPS battery performance test under different battery configurations and it has better economical efficiency and versatility.