Abstract: In the conventional fatigue test, manual measurement of fatigue crack size has low work efficiency and high probability of fault, and the data can not be digitally managed. The crack morphology was identified by image measuring instrument, and the geometrical dimensions of fatigue cracks were measured automatically in arranging sequence and order of samples reasonably. The practice show that the automatic measurement method can be used to measure the fatigue cracks geometrical dimensions of various metallic materials fatigue fracture samples under the demand of mass inspection.