Abstract: With the large⁃scale development of ultra⁃deep tight sandstone gas reservoirs，shale gas reservoirs and other unconventional gas reservoirs，the problems of unconventional reservoir permeability testing have been gradually high⁃ lighted，such as difficulty，long time and low precision. In order to improve the accuracy of measuring reservoir rock permeability under the conditions of high temperature and high pressure，this paper，based on the principle of high⁃ pressure pulse permeability testing，assumed the reservoir as one⁃dimensional compressible fluid，and the rock is com⁃ pressible under high pressure. This paper optimized the control equation solution process， and deduced an im⁃ proved complete and practical expression of high pressure pulse permeability. Considering a high⁃temperature and high⁃pressure formation environment of the reservoir，the pulse permeability test experiment of high temperature and high pressure was designed and carried out. The concept of pressure difference retention degree was proposed for the first time to reveal the variation characteristics of pressure pulse decay in different periods. The error analysis of high⁃pressure pulse permeability and pore pressure，pressure difference retention degree，conventional Klinkenberg permeability，and conventional pulse permeability were carried out. The results show that the experimental data of pres⁃ sure difference decay can be used to accurately calculate the pulse permeability of rock samples with pressure differ⁃ ence retention degree ranging from 20% to 50%. The effective stress remains unchanged，the rock samples with differ⁃ ent permeability ranges are affected differently by high pore pressure. Compared with other permeability，the high⁃pres⁃ sure pulse permeability is closer to the actual permeability of the rock under the high⁃temperature pressure formation environment. This permeability testing method is fast and accurate，and has its unique advantages，which is an effec⁃ tive method for testing and evaluating the physical properties of deep unconventional gas reservoirs.