Heat source of tunnel regeneration high power semiconductor laser has been discussed. Two-dimension transient thermal distribution of this kind of laser diode at pulse work is simulated by using the finite element method, and the wavelength shift is measured and converted to temperature rising value at different time, the calculated results are in agreement with the measured data. It is found that the temperature rising of the active region close to the substrate is higher than that of the active region close to the heat sink, and using the diamond-copper heat sink to replace the copper heat sink could reduce the inner temperature rising of laser diode greatly, and make tunnel regeneration high-power semiconductor laser working with high efficiency.