Magnetic core loss is one of the important parameters of power magnetic components. In view of the problem that AC power method has a large error in measuring the core loss at high frequency and low loss angle, as well as the disadvantages of calorimetric method, such as high time cost and tedious measurement process, DC power method is proposed. The DC method obtains magnetic core loss by measuring DC input power of inverter circuit, greatly weakening the impact of impedance angle of the measured magnetic component on measurement accuracy, and can accurately measure magnetic core loss under PWM wave excitation. This article conducts research on the following aspects: Firstly, based on the DC power method, this article measured the losses of magnetic cores under asymmetric PWM wave and symmetric PWM wave excitation, established a prediction model for magnetic core losses, and verified the accuracy of the model. Verify the existence of relaxation loss when measuring the magnetic core loss under symmetric PWM wave excitation, and establish a relaxation loss prediction model.