The invention discloses a roller cold-work hardening contact fatigue microscopic crack detection method, and belongs to the technical field of roller nondestructive testing method; the method is used for detecting cold-work hardening contact fatigue microscopic cracks of a roller in a rolling mill. The method comprises the steps: detecting a measured support roller discharged out of a machine by an ultrasonic flaw detector and a probe, firstly, calibrating the measured support roller, and preparing a DGS curve; then carrying out circumferential and axial scanning on a roller body of the measured support roller; and carrying out fatigue crack qualitation, fatigue crack quantification and fatigue crack positioning on the roller body. The detection method has the remarkable advantages of being safe, reliable, flexible, convenient, and simple to operate, provides a novel and practical detection technology for detection of fatigue cracks of a roller of a hot rolled strip rolling mill, fills up a blank of the cold-work hardening contact fatigue microscopic cracks of the hot-rolled roller, can effectively avoid deepening and development of the fatigue cracks, significantly reduces the production cost, improves the economic benefits, and has great popularization and use values in the industry.