In large-scale high-power laser system, real time detecting is of great importance to laser energy transmission. There are a large number of beams and they are distributed in a large area, furthermore, intensive electromagnetic disturbing affects the linearity of the laser energy detecting severely. A method of measuring laser energy is introduced in this paper, which uses thermopile to change the laser energy, and analogue digital module to process the signal. Subtracting the background and compensating the potential to overcome the effects of the temperature drift is focused on. Optimizing linearity result is achieved in this paper. The linearity of laser energy measurement has been optimized to more than 2% in our method.