A power measuring apparatus including a voltage transformer, a voltage-current measuring circuit, and an operation unit is provided. The voltage transformer converts an input voltage signal into an output voltage signal. The voltage-current measuring circuit includes an inductor, a first resistor, a first capacitor and a second capacitor. A first end of the first inductor herein receives the output voltage signal and a second end thereof generates a voltage feedback signal. The operation unit performs an operation on the voltage feedback signal and a terminal current signal between the first terminal and the second terminal of the first capacitor so as to calculate a power signal. In this way, the accuracy of thermal test is effectively increased by the presented invention.