Abstract: The basaltic tuff from Derong County, Sichuan Province, is selected for the tests with a high confining pressure of 200 MPa and temperatures from 200 to 800?C. The test results of 7 specimens are obtained and show that the Young’s modulus and yield strength of the rock specimens decrease when the test temperature rises and the confining pressure is constant. When the test temperature reaches 700?C, the major failure mode of the rock specimens is rheology. The test temperature of 400?C is the critical temperature for remarkable charge of the mechanical performance of the rock specimens. The results of X-ray dissipation analysis indicate that the mineral contents of the clay in the test specimen decrease as the temperature rises and exceeds 400?C, but the plagioclase and calcite contents increase. When the temperature exceeds 500?C, a new mineral, olivine, appears in the rock specimen. The SEM photos of the rock specimens show that before 400?C, it is very difficult to find out micro fractures in the rock specimens, but when the test temperature reaches 700?C and 800?C, the partial melting phenomenon occurs in the rock specimens, at the same time, when the test temperature reaches 800?C, the recrystallization phenomenon occurs. The macro mechanical performance of the rock specimens corresponds very well to the change of micro textures and mineral contents. The research findings agree with the others and give some explanations for the response mechanism of the mechanical performance of rock specimens under high temperatures and high confining pressures from the view point of micro texture and ingredient.