Abstract: Gradient test of Vickers hardness is required at the positions of weld, heat affected zone and base material in process evaluation for cast steel welding. Space between dents shall be equal, and they shall be aligned in a straight line.HV-120 Vickers hardness tester was selected for the test, and two square magnets were the tool to fix sample, vernier caliper shall be used to maintain the accuracy of space between dents. The operation is simple and feasible. It can assure the specimen move in a straight line, and reduce the space deviating between dents to ±0.02 mm.By doing so, a clear diagonal line and reliable value can be obtained, and it meets the requirement of specification.