Abstract: The hardness, crack morphology and microstructure of U71Mn steel rail gas pressure welded joint after service were tested and observed by hardness tester, profilometer, optical microscope and scanning electron microscope. The damage behavior in different regions of the joint was analyzed. The results show that the depressions were located at 30-50 mm away from the joint center on both sides, and their positions were consistent with the softening zones in the joint. The hardness of the joint increased because of wheel-rail contact, but the hardness of the softening zone was always lower than that of the base metal. According to morphology of pearlite, the joint was divided into four regions from the joint center to heat-affected zone on both sides: lamellar pearlite area, partial pearlite spheroidization area I, pearlite spheroidization area and partial pearlite spheroidization area Ⅱ. The softening zone was located in pearlite spheroidization area. The depths of cracks and the expansion angles of crack tips in pearlite spheroidization and partial pearlite spheroidization areas were relatively large, because of the relative small resistance of granular pearlite to crack growth.