As a kind of unconventional oil and gas resources, shale oil and gas resources are difficult to exploit and have low economic benefits due to their low porosity and permeability. In recent years, microwave as a new heating technology in shale oil and gas production has gradually been paid attention to and carried out a series of studies. Microwave thermal effect can destroy the rock structure, improve the permeability of oil and gas effectively, reduce the difficulty of extraction, and study the process and mechanism of thermal damage of shale under microwave irradiation is of great significance to the exploitation of shale oil and gas resources. In this study, the self-made microwave heating equipment was used to carry out irradiation tests on shale, and the influence of irradiation temperature (500-900°C) on shale structure damage was investigated. The microstructure of shale under microwave irradiation and the evolution of mineral crystal phase were revealed by means of scanning electron microscope, X ray diffraction spectrometer (XRD), X ray fluorescence spectrometer (XRF) and comprehensive thermal analyzer (TG-DSC), and the relationship between microwave irradiation temperature and its porosity was established. It is shown that microwave irradiation can cause irreversible thermal damage to shale, increase the cracks and pores of shale, open the percolation channel for shale oil and gas migration, and reduce the difficulty of exploitation of shale oil and gas resources. The results of this study are of great significance for the development of shale oil and gas resources by microwave heating.