The work aims to reduce the effects of erosion phenomenon on material surface in high-pressure water jet strengthening technology. Single factor test was applied to 18CrNiMo7-6 carburizing alloy steel by selecting water jet pressure, jet target distance and covering small steel ball diameter as variable parameters. The tested materials were measured and analyzed by means of three dimensional surface morphology measurement system and X-ray residual stress analyzer. Surface roughness increased as the pressure increased, and the maximum residual stress was 693 MPa. However, residual compressive stress decreased as injection pressure further increased. With the increase of target distance, surface residual stress decreased almost linearly, the surface roughness reached the minimum value of 0.77 μm at the target distance of 110 mm. As small steel ball diameter increased, the surface residual compressive stress first increased and then decreased, and the maximum value was 782 MPa; the surface roughness first decreased and then increased, and the minimum value was 0.76 μm. Both surface roughness and residual stress of 18CrNiMo7-6 steel are obviously affected by water jet injection pressure, injection target distance and covering small steel ball diameter. Meanwhile, each parameter has different influence mode on material surface in different variation range, and different influence on surface roughness and residual compressive stress of materials.