On the basis of the cylindrical grinding-hardening test, the influences of the grinding parameters on surface hardened layer were studied. The result shows that when ap≤0.2mm, there is an unhardened area exist in cylindrical grinding hardened workpiece. When ap＞0.2mm, there is a tempered area exist in cylindrical grinding hardened workpiece due to the action of grinding heat during cut-in and cut-out of grinding wheel. When depth of cut increases, or feed speed decreases, the hardened layer depth increases accordingly. In the practical application, the satisfactory quality of the cylindrical grinding hardened layer can be obtained through reasonable combination of ap and vw.