Static uniaxial compression tests were carried out on five groups of GCC samples with different rock proportions (0.4, 0.5 and 0.6) after treatment at 25 °C, 200 °C, 300 °C, 400 °C and 500 °C, as well as granite and concrete monomers. In order to explore the static compressive mechanical properties and failure evolution law of GCC after high temperature, the compression fracture of the connection surface of the GCC specimen was tested by SEM scanning electron microscope. The results show that the peak strength, elastic modulus and mass of GCC specimen are between concrete and granite, and are positively correlated with the proportion of rock. In the deterioration of strength, the concrete part dominates, the total stress-strain curve gradually slows down, the suddenness and brittleness of failure weaken, and the graduality and plasticity gradually increase. With the change of temperature, the failure modes of the assemblage are different, and the "Y" type shear failure of concrete and granite splitting failure are the main ones, and the number of microcracks increases during failure. The results of this study can provide some theoretical support for the safety assessment of underground engineering after fire, and also lay a certain theoretical foundation for engineering design and monitoring in complex environments.