In order to explore calcium aluminate cement (CAC) and wollastonite (WS) synergistic modification effect, 13 groups of modified magnesium potassium phosphate cement (MKPC) specimens with different mix ratios were designed by compounding CAC and WS in this paper. The corrosion resistance and microscopic characteristics of modified MKPC under the action of NaCl, MgSO4, NaOH and H2SO4 solutions were studied. The results show that the reaction product of CAC is coated on the MKPC hydration product magnesium potassium phosphate hexahydrate (MgKPO4·6H2O) in the form of amorphous aluminum gel and fill in the pores between MgKPO4·6H2O crystals, which improves the microstructure of MKPC and inhibits the corrosion of corrosive media. As an inert component, WS does not participate in hydration reaction of MKPC, but makes the pore structure of MKPC denser by filling. The synergistic effect of CAC and WS can effectively improve the corrosion resistance of MKPC in NaCl and MgSO4 solutions. When the content of CAC and WS is 15% and 5% of the mass of cementitious material, the improvement effect is the best. In NaOH and H2SO4 solutions, the CAC reaction products filled between MgKPO4·6H2O crystals are corroded, resulting in the formation of interconnected channels between crystals, which affects the improvement of corrosion resistance.