Based on the heat transfer model of vertical external cavity surface emitting semiconductor laser with heatspreader, the change in temperature of the quantum well active region has been calculated under different conditions with the finite element method. The equivalent thermal resistance model has been proposed and calculation formula has been derived for the maximum temperature of quantum well, the parameters of which are determined by fitting curves. The calculation shows that the maximum temperature of the quantum well increases linearly with the pump power, while it is nearly inversely proportional to the light spot area. The heatspreader can significantly reduce temperature and its unevenness in the active region of the quantum well. The equivalent thermal resistance model shows that a larger thermal resistance forms due to the difficulty of heat flux to spread in the radial direction, thus thermal diffusion capacity of the heatspreader tends to saturation. As a result the thermal performance of silicon carbide is approximately 75% of that of the diamond.