Thermal aberrations are the main impediments for high-energy transverse multimode lasers to achieve high brightness and beam qualities. To address this issue using adaptive optics, traditional wavefront sensing methods have great limitations for aberration correction in high-energy transverse multimode lasers, because these lasers are no longer point sources. The general extended-object wavefront sensor (GEWFS) invented by the authors can work with extended sources in real time, and it is highly suitable to solve this problem. The application of the GEWFS into the compensation of thermal aberrations in a high-energy laser is preliminarily investigated by means of a simulation experiment. In this simulation experiment, a transverse multimode laser diode simulates a high-energy laser, a and phase plate thermal aberrations, which is compensated by a closed-loop adaptive optics system mainly composed of the GEWFS and a membrane deformable mirror. Simulation experimental results show that the peak intensity of the laser beam image is improved about 2.35 times, and the approximate Strehl ratio of the laser system attained 0.90. The results indicate that the GEWFS is simple and accurate enough for wavefront sensing from extended sources, and it will greatly expand the application fields of adaptive optics.