Abstract: During the development and drilling of oil and gas resources and deep geothermal energy, many problems such as extremely high rock hardness and poor drillability may be encountered, and it is difficult to improve drilling efficiency by traditional drilling techniques. To solve this problem, the principle underlying rock breaking by plasma torch were analyzed. On the basis of it, rock spallation, melting, and evaporation were found to be the main methods for rock breaking. Laboratory tests were carried out to determine the effect of using plasma torch for breaking basalt samples and granite samples with different thicknesses. It was demonstrated that plasma torch can burn through 50 mm thick basalt sample and 30 mm thick granite sample, but could not burn through thicker rock samples. Combined with the test results, the problems existing in the field application of plasma torch drilling technology were analyzed, and research and development suggestions were thereby advanced. The results of this study can provide reference for the research and application of plasma torch drilling in deep hard formations.