Abstract：A 20 MN servo-controlled rock triaxial testing system with high temperature and high pressure developed by the authors is introduced. The system is constituted with main loading sub-system，high temperature control sub-system，sample assembling sub-system，and measuring system. The maximum axial pressure and confining pressure are both 10 000 kN. The maximum sizes of tested cylinder sample can be set as large as f 200 mm×400 mm. The heating temperature can reach as high as 600 ℃. Some related key issues and corresponding solving methods in the test system are also introduced. Compared with high temperature and high pressure test machine of geophysics，the developed test system has some advantages as follows：(1) Larger size sample can be tested，and the volume of the largest sample is 64 times larger than ordinary one and some properties of rock mass can be discovered thoroughly. (2) The servo-controlled system can measure the deformation of sample under different temperatures easily. (3) The thermo-physico-mechanical process of heated rock samples can be measured. (4) Drilling process in deep underground with high temperature can be simulated and investigated. (5) It can be used to study engineering characteristics of rock mass. Certain experimental investigations on coal samples with high temperature and high pressure in the system demonstrated that the plastic properties of the coal sample were enhanced and the Young¢s modulus decreased with temperature. The relationship of the Young¢s modulus with temperature is found with exponential rule. The testing system can be used to investigate certain scientific natures of deep mining process，direct liquefaction and gasification of coal，geothermal excavation，mine safety，construction safety，etc..
