Abstract: In order to evaluate the influence of alternating ultra-high temperature on the mechanical property and microstructure of set cement in a heavy oil thermal recovery well more accurately, this paper designed a set of ultra-high temperature water wet simulation curing device and method based on the actual downhole environment of set cement. And based on this, the change laws of the compression strength of set cement under dry combustion environment and water wet environment were studied. In addition, the influence of different curing environments on the physical composition, chemical structure, pore structure and micromorphology were explored by means of XRD, TG, nitrogen adsorption and SEM technology. It is experimentally indicated that after set cement is cured 7 rounds under alternating ultra-high temperature, its compression strength under the dry combustion environment decreases by 17.7% from 28.7 MPa to 23.62 MPa; but in the water wet environment, it decreases by 6.3% from 29.54 MPa to 27.68 MPa, which is 14.67% higher than the value in the dry combustion environment. Furthermore, the set cement in the water wet environment has high hydration product content, small pore diameter, low porosity and compact overall structure. The research results can provide technical support and theoretical guidance for the performance evaluation of set cement in heavy oil thermal recovery wells and is of great significance to enhance the safe and efficient development of heavy oil resources.