The ultrasonic hardness tester is composed of handheld PDA and Cui measuring probe. The two are connected by cables. The diamond indenter at the front end of the hardness tester contacts with the measured part. Under uniform contact pressure, the resonance frequency of the probe changes with the hardness. The purpose of hardness measurement is to measure the frequency change. The workpiece parts that can be measured by ultrasonic hardness tester include flange edge and gear root stamping parts; die, thin plate; surface hardened teeth and gears; taper part hardness measurement; shaft and thin-wall pipe and container measurement; wheel and turbine rotor hardness measurement; drill head edge hardness measurement; welding parts.