The excellent physical and electronic properties of silicon carbide recently made it to be the mainly focused power device material for high-temperature high-power and high-frequency application. In this study, thermal analysis model is established through simulation method ANSYS 14.0, studying the factors affecting the thermal resistance of PiN diode. Increasing the area of the device or decreasing the thickness of the chip and the solder layer can reduce the thermal resistance effectively. At last, we give a thermodynamic model of the device in Sentaurus TCAD software, modelling the temperature phenomenon and self-thermal effects on performance degradation of 4H-SiC PiN diode, finally, we analyse and forecast the failure mechanism of similar silicon carbide devices. Results show that the higher the temperature, the higher the heat flux generated by the section of the device will be to promote temperature, and the smaller the temperature gradient inside and outside the device which leads to heat conduction, hence resulting in increased current degradation.