In order to further explore the erosion properties of wollastonite-slag-metaalkin-based polymer mortar under multi-factor coupling, a systematic experimental study is carried out. The changes of mass loss rate, compressive strength and flexural strength of mortar under the coupling conditions of alternation of drying and wetting and seawater erosion are analyzed by experiments, and the influence mechanism of each factor on the mortar performance is further analyzed, and the corresponding strength prediction model is constructed. The results show that: 1) With the increase of the number of coupling times between alternation of drying and wetting and seawater erosion, the mass loss rate of mortar shows an upward trend, the flexural strength gradually increases, and the compressive strength shows a trend of first increasing and then decreasing. 2) The concentration of alkali exciter has a promoting effect on the erosion resistance of the polymer mortar under the multi-factor coupled erosion scenario, among which A30 performs the best. 3) After 90 times of alternation of drying and wetting and seawater erosion, the mass loss rate is only 4.55% , the flexural strength reaches 22.3 MPa, and the compressive strength reaches 67 MPa. 4) The immersion method has a certain impact on the strength of the mortar, and the full immersion test block shows higher strength and better erosion resistance. 5) The strength prediction model based on the relative strength of mortar can effectively characterize the correlation between the relative strength of wollastonite-slagmetakaolin-kaolin based polymer mortar under the coupling of alternation of drying and wetting and seawater erosion, and provide reference for its application in practical engineering.