Abstract: In order to guarantee the safe operation of a new research reactor in China, the design criterion, system structure, function and equipment composition of Emergency Power System of the reactor are introduced, and the key elements are analyzed, which should be considered in the capacity determination process of diesel generator set, uninterrupted power supply(UPS) and Class 1E batteries. An Emergency Power System was designed as a special safety facility of the new research reactor, and then its capacity were calculated. The results show that the capacity of diesel generator set is 1000 kV?A, the maximum capacity of UPS is 600 kV?A, and the maximum capacity of Class 1E batteries is 5000 Ah. When the two outside powers are lost, this emergency power system can supply 72 h power to the reactor safety system continuously, and it can guarantee the safe operation of the reactor.