Abstract: In order to reveal the mechanical degradation mechanism and the whole process deforma⁃ tion response law of coarse-grained marble under high temperature thermal damage，and to improve the de⁃ fect that the traditional rock yield hardening constitutive model cannot characterize the pore compaction stage，the SX2-12-10 high temperature box resistance furnace is used to carry out the gradient high tem⁃ perature heat treatment of coarse-grained marble specimens at 25 ℃，200 ℃，400 ℃ and 600 ℃，and the complete stress-strain curve of rock under different thermal damage degrees is obtained by uniaxial com⁃ pression test. The test results show that with the increase of heat treatment temperature，the thermal dam⁃ age degree of coarse-grained marble increases，the elastic modulus and uniaxial compressive strength de⁃ crease significantly，and the continuous deformation characteristics of pore compaction stage in the initial stage of loading become more obvious. Based on the statistical damage theory of rock and Drucker-Prager strength criterion，the yield hardening constitutive model of foundation is constructed. The Sigmoid func⁃ tion is introduced to add the pore compaction correction term，and an improved constitutive model which can fully describe the four-stage deformation characteristics of rock is established. The fitting results show that the fitting accuracy of the optimized model is significantly improved，and the model parameters change regularly with the evolution of thermal damage. The parameters a，m and b gradually decrease with the in⁃ crease of temperature，and the parameter c gradually increases. Through the parameter sensitivity analysis by the control variable method，it can be seen that the parameters a and m mainly control the curve shape of the yield hardening and strain softening stage of the rock mass，and the parameters b and c accurately control the development rate and critical strain of the pore compaction stage. The optimized constitutive model has a simple form and clear physical meaning of parameters. It can truly reproduce the whole pro⁃ cess of mechanical behavior of pore compaction，linear elasticity，yield hardening and strain softening of high temperature damaged marble，which can provide theoretical reference for the stability analysis of high temperature rock mass engineering.

Key words: high temperature damage, coarse-grained marble, constitutive model, pore compaction, Sigmoid function, parameter sensitivity analysis