Abstract: In order to further reveal the mechanism of chloride erosion to cement matrix composite materials under dry-wet cycling, the resistance to chloride erosion of two kinds of water to cement ratio of cement concrete, mortar and paste specimens under dry-wet cycling were studied. It is found that dry-wet cycling can promote the intrusion speed of chloride ions and increase its invasion depth and concentration. With the increase of water to cement ratio, the above effect of dry-wet cycling gets more obvious. Furthermore, the incorporation of slag can increase the resistance to chloride erosion of cement matrix composite materials and reduce the invasive effect of dry-wet cycling. Meanwhile, the corresponding micro-structural changes before and after chloride erosion under dry-wet cycling show that Friedel's salt is obvious on the surface of paste samples of cement matrix composite materials and adding slag significantly increases the formation of Friedel's salt in the sample.