The invention discloses an assessment method for the heat reliability of a high-electron-mobility transistor. The problem that assessment of the heat reliability of a device is inaccurate with an existing method is mainly solved. The assessment method in the technical scheme includes the steps that 1) output characteristics of the device at different temperatures are measured with the pulse method, and the variation relationship of saturation drain currents along with the temperatures is extracted to serve as a calibration curve; 2) the output characteristics of the device at indoor temperatures are measured with the direct current method, and average temperatures of a device channel at different powers are extracted in cooperation with the calibration curve; 3) based on all parameters ofthe measured device, through finite element software ANSYS, a three-dimensional finite element heat model is established, and test results under the different powers are compared with the channel average temperatures obtained after simulation, and the accuracy of the model is verified; 4) the junction temperature and heat distribution of the device are led through model simulation, peak-value heatresistance is calculated, and assessment of the heat reliability of the device is achieved. The assessment method is high in assessment accuracy of the heat reliability, easy to operate and suitablefor high-electron-mobility transistors with multiple structures.