Abstract: Solving the magnetic loss under non-sinusoidal conditions accurately and efficiently is of great significance to the heating analysis and optimal design of electrical equipment. The pulse width modulation (PWM) excitation characteristic test system was established to study the calculation method of magnetic loss of ferromagnetic materials under PWM excitation. The hysteresis characteristics and loss characteristics of silicon steel sheets under different working conditions were measured. Based on that, the influence of PWM excitation characteristics (waveforms of voltage and magnetic flux density and modulation index) on each loss component is analyzed. At the same time, the hysteresis process during PWM excitation is analyzed, combining with the influence of magnetic relaxation processes on residual loss, an improved loss separation model under PWM excitation characteristics and magnetic relaxation was proposed, which can effectively calculate the magnetic loss. The simulation and experimental results show that the improved loss separation model in this paper has high accuracy and engineering applicability.