Abstract: Sampling examination by metallographic test was the traditional method for measuring the depth of the quenched layer in crankshaft, which could not meet the needs of the production of auto industry. Ultrasonic scattering echo method was used to measure the depth of the quenched layer in Commins crankshaft. It was showed by laboratory and on-site tests that ultrasonic nondestructive testing could be applied to the measurement as a substitute for metallographic examination. The measuring error was ≤0.3 mm.