To improve the water resistance of magnesium oxysulfate cement （MOSC）， MOSC were prepared using calcined zeolite powder as an admixture. The effects of calcined zeolite powder before and after calcination on the setting time， mechanical properties， water resistance， phase composition， microstructure， and pore structure of MOSC were investigated. The results indicate that the mechanical properties of MOSC are improved by adding calcined zeolite powder， and the hydrated magnesium silicate gel can be formed by the reaction of zeolite powder before and after calcination in the MOSC system， which reduces the total porosity of MOSC and improves the water resistance of MOSC， but the water resistance of MOSC mixed with calcined zeolite powder is better. After adding 20% zeolite powder that has been calcined at 200 ℃ and treated at a heating rate of 15 ℃/min， the water resistance of MOSC is optimal. The retention coefficients of compressive and flexural strength at 28 days can reach 0.91 and 0.95， respectively.