Abstract: To enhance the mechanical properties of magnesium oxysulfade (MOS) cement, wollastonite powder (WS) was utilized as an additive before and after calcination to study its effect on the mechanical properties of MOS. The WS and WS/MOS composite system before and after calcination (1000℃) were analyzed by DSC-TG, XRD, FTIR, NMR, SEM, and mercury intrusion porosimetry (MIP). The results show that calcination stimulates the hydration activity of ²⁹Si in WS, and the calcined WS stimulates its hydration activity in magnesium alkali environment, resulting in better performance of WS/MOS composite materials. WS enhances the mechanical properties of MOS, and the strength of WS/MOS composite system with the calcined WS increases more significantly. The bending strength and compressive strength of MOS on the 28 days reach their maximum values when the after calcination WS content is 20wt%, which are 11.4 MPa and 63.4 MPa, respectively, with increments of 71.4% and 21.2%. WS optimizes the pore structure and reduces the proportion of pores larger than 100 nm in MOS. The calcined WS has good interface compatibility with MOS, which is more conducive to improving the mechanical properties of MOS.