An equivalent load test based on DC injection is designed to allow the temperature rise of the induction motor at rated load to be determined experimentally from a single test at conditions other than rated load. This method is often used in the cases of special machines with inaccessible free shaft ends, high-speed machines or vertical machines. According to this principle, a set of 24-position thermal test device with AC and DC power supply circuit is designed. The device injects continuous and adjustable DC current while supplying AC power to the motor, increases the effective value of current in the motor winding, realizes equivalent load, and completes the thermal test of the motor. The test shows that the standard deviation of the DC injection equivalent load method is slightly larger than that of the direct load method, and the uncertainty is within an acceptable range. This device can be used in the accelerated thermal aging test of the motor to analyze its insulation performance and obtain the expected life of the motor.