Abstract: High energy laser (HEL) meter by means of calorimetric method is used to measure continuous wave (CW) laser with energy more than 50 kJ. The photoelectricity calibration is usually made by CW laser illumination with known power for more than 20 minutes, and because of the heat loss, the uncertainty is up to 12%. The influence of heat radiation and heat convection on energy measurements of CW high energy laser was analyzed theoretically based on the model of calorimetric plane absorbing HEL energy meter. The cooling down model for laser energy meter with plane absorbing chamber was deduced accurately which made it possible to compensate for heat loss of energy meter. The experiments apparatus was established to verify the correctness of the model. With this model, the measurement uncertainty of photoelectricity calibration decreases to 1% above.