In order to evaluate the durability of magnesium phosphate cement under the action of dry-wet cycle and reveal the deterioration mechanism, 20, 40 and 60 dry-wet cycle tests were carried out on the magnesium phosphate cement samples, and the deterioration process and crack propagation law of macroscopic strength and deformation parameters were described by uniaxial compression test and X-ray tomography (CT), and XRD, thermogravimetric and SEM tests were used to characterize the changes of phase composition, hydration product content and morphological characteristics. The results show that in the early stage of the dry-wet cycle, the compressive strength and elastic modulus of magnesium phosphate cement increase due to the secondary hydration, and then gradually decrease with the increase of the number of dry-wet cycles, and the failure mode changes from brittle to plastic. Due to the increase of crack and pore connectivity induced by the dry-wet cycle, the fracture mode changes from tensile failure to tensile and shear failure. The deterioration mechanism of magnesium phosphate cement is mainly controlled by the dissolution, thermal expansion and dry shrinkage and wet expansion caused by K-type struvite.