The invention relates to a test device for the thermal capacity of a closing resistor of a high-voltage circuit breaker. The test device comprises an insulating cylinder, and is characterized in that two ends of the insulating cylinder in the axial direction are respectively provided with a first sealing end cover and a second sealing end cover, the inner side of the first sealing end cover is provided with a resistor bracket used for installing the closing resistor, the bottom end of the resistor bracket is provided with a resistor connecting base provided for crimping and conductive connection of the end face of the closing resistor, and the top end of the resistor bracket is fixedly provided with a conductive joint in a detachable manner. The test device further comprises a conductive supporting body which is used for being supported between the conductive joint and the closing resistor so as to compensate the axial spacing of the conductive joint and the closing resistor. The inner side of the second sealing end cover is provided with a conductive base which is in inserting conduction or crimping conduction with the conductive joint. The two ends of the insulating cylinder in the axial direction are respectively provided with a first wiring terminal and a second wiring terminal which are in conductive connection with the resistor connecting base and the conductive base respectively. The test device is good in adaptability, so that different test devices are not required to be designed for different voltage classes or different sizes of closing resistors, the cost can be effectively reduced, and the use is convenient.