As the typical load with thermal energy storage property, thermostatically controlled loads possess the potential to actively participate in active power dispatch and control for power system. In order to facilitate the analysis and control, a numerical inverse Laplace transform solving method of thermostatically controlled load group’s Fokker-Planck equation aggregation model is proposed. The single model and Fokker-Planck equation aggregation model for thermostatically controlled loads are introduced respectively, and the aggregation model’s numerical inverse Laplace transform solving method is proposed. Simulation results verify the effectiveness of the proposed numerical inverse Laplace transform solving method. A decentralized control scheme is applied to controllable load, which adjusts its setting temperature to regulate its power demand according to frequency measurement signal. The numerical inverse Laplace transform solving model is integrated into frequency control model of 3 machine 9 bus power system, verifying the effectiveness of the frequency control effects. This work is supported by National Natural Science Foundation of China (No. 51507094).