In order to investigate the effect of WC grain size on coatings’ properties and abrasive wear performance, a few WC-20Cr3C2-7Ni coatings with three different WC grain sizes were deposited by the high-velocity oxy-fuel (HVOF) thermal spray process. The phase compositions, microstructures, and mechanical properties of the coatings were investigated. Furthermore, the two- and three-body abrasive wear performances of the three coatings were tested by using SiC and SiO2 abrasives, respectively. The results show that all the three coatings were composed of WC, Cr3C2, and the Ni binder as well as the (W,Cr)2C phase. The abrasive wear resistance of the WC-20Cr3C2-7Ni coating monotonously increased with increasing WC grain size when the SiC abrasive was used in the two- and three-body abrasive wear tests. However, the wear resistance trend was reversed when the SiO2 abrasive was used in the three-body abrasive wear test. The specific wear rate of the WC-20Cr3C2-7Ni coating exposed to the SiC abrasive under the two-body abrasive wear test was the largest. The wear resistance of the coatings was more significantly affected by the hardness of the abrasive particles than the size of carbides present within the coating. The high hardness of SiC can cut both the carbide and the binder phase of the WC-based cermet coatings, resulting in a high wear rate, whereas the low hardness of SiO2 cuts and/or scratches the binder initially, and then it dislodges the carbides from the matrix. The dislodged carbides which were subsequently pulled out from the matrix by the repeated impact of the SiO2 abrasives result in a milder wear rate.