Abstract: In order to apply a microwave rock breaking technology in petroleum drilling, the influences of HTHP on the microwave rock breaking result during drilling were studied. According to the microwave absorption characteristics of rock components, a two-dimensional plane model of a rock was established, and the influences of temperature, confining pressure and the combination of both the two on microwave rock breaking result were simulated. The study result found that under the same microwave irradiation parameters, the plastic deformation time of rock shortened with the increase of downhole temperature, and the plastic deformation time of rock increased with the increase of downhole confining pressure. Considering the combined results of both temperature and confining pressure, the influence of confining pressure was dominant, while the effect of temperature mainly exerted under high temperature conditions. The results showed that the confining pressure did not result in microwave rock breaking, and the influence was obvious; temperature had a certain promotion effect on microwave rock breaking, but such an effect was evident only under high temperature conditions. Therefore, when applying microwave in rock breaking, it is necessary to comprehensively consider the influences of temperature and confining pressure on rock breaking results, and to adjust the microwave parameters in time to make the rock breaking more economical and efficient.