The invention belongs to the safe nondestructive detection technology field, and in particular relates to a railway micro-magnetic flaw detector and an inspection method. A micro-magnetic defect magnetic charge mutation detection principle is adopted by the railway micro-magnetic flaw detector to make the defect detection realized. The railway micro-magnetic flaw detector consists of a magnetic sensor device, a signal preprocessor, an A/D converter and a computer system. The magnetic signals leaked because of defects are detected by the sensing device, converted into electric signals and inputinto the signal preprocessor. The signals are amplified, filtered and purified by the signal preprocessor, transmitted into the A/D converter and are transformed into digital signals. Then, digital filter, signal analysis, defect estimation, defect calculation and display record are implemented on the signals by the computer and are controlled by the computer to detect defects. The flaw inspection method is used for detecting the railway damage defect. The defect detection reliability is two times higher than a traditional nondestructive method. And the working efficiency is improved by fivetimes. At the same time, a worldwide problem that no effective method can be used for turnout inspection at present is solved.