In order to acquire the laser coupling coefficient of a metal plate, an inversion method was given based on measured temperature data on the rear surface of the plate. By introducing some approximate conditions, the inversion expressions of the laser coupling coefficient and the temperature on front surface were derived, and a engineering algorithm of laser coupling coefficient was obtained. The inversion algorithm was validated by using two methods. one is to calculate the 1.3 μm laser coupling coefficeint of the 30CrMnSiA by reversal method and to compare it with the experiment result in references for the same material plate;the other is to measure the temperature rise on the rear surface of the plate and to obtain the changes of the coupling coefficient with the radiation time and temperature and compare it with the measured experiment result in our experiments for the same material plate. The verified result shows that the inversal engineering algorithm is feasible and meets the requirement of the study of laser irradiation effects.