A new method of rating cooling capacity of room air conditioner has been introduced. Two measurement systems (electric heat belance and enthalpy difference method) are combined into a same testing device. The new method is a improvement of air-duct heat balance method. The measurement value of cooling capacity which is got from the electric heat can be checked by use of the enthalpy difference method. The devices can be used to measure heating capacity of room air-conditioner in heat pump. operation. Testing results have been compared with rating Values of the national authoritative measurement set. At last, the errors of testing data have been analysed briefly.