Cement is prone to seal failure under complex load conditions. For oil and gas wells, such as hydraulic fracturing, steam injection or other operation, the stress situation of the cement sheath will change. The cement sheath and the casing and the formation in the stress-strain relation change, forming a micro ring gap, or cause internal damage in the cement to form micro cracks and increasing permeability, resulting in the loss of the sheath seal, which affects the safety and life of oil and gas wells. The failure of cement sheath seals not only increases the cost of subsequent drilling, completion and production increase, but also affects the period of well construction, the safe exploitation of oil and gas and the production capacity of the oil field, which may cause complete well rejection and even the loss of personnel and environmental damage. In order to deal with this problem, the industry has studied the failure of cement sheaths under various loads, and some mature theories have been obtained for the study of conventional cement. The damage of cement and the change of permeability under the condition of cement load are relatively rarely studied. Based on the experiments on the stress and strain relationship of cement under different loading methods, the failure mechanism of cement is explored and studied in combination with permeability and acoustic emission monitoring.