Abstract: The thermal stress of power semiconductor devices is a significant contributor to their failures, so thermal modeling of devices has received increasing attention in recent years. Due to the complexity of operating conditions, the thermal stress of power semiconductor devices has different characteristics under different timescales, making it difficult to model. To address this issue, many efforts have been undertaken in recent theses years, and frequency-domain modeling is a relatively simple and practical approach. However, most existing methods only focus on the temperature characteristics of the device while ignoring the heat flow characteristics, which leads to inaccurate temperature prediction when the device's thermal model is connected to external heat dissipation conditions. In this paper, the low-pass filter characteristics of heat flow in power semiconductor devices are first analyzed by frequency-domain analysis, and proposes a multi-order three-frequency low-pass filter to describe the device's thermal flow characteristics. The multi-order three-frequency low-pass filter is able to describe the thermal flow characteristics of the power semiconductor device in full frequency band. The proposed approach improves the accuracy of device thermal stress description and solves the problem of connecting the device model with external heat dissipation conditions. The proposed method is validated through finite element simulation and experiments.