Abstract: The butt welding test of 30 mm thick high strength and toughness medium-Mn steel plate was carried out by CO₂ gas shielded welding. The stress amplitude-life curves of medium-Mn steel welded joints were obtained by round bar tensile and compressive fatigue test. The high cycle fatigue limit was measured and its fracture morphology was observed. The results show that the high cycle fatigue limit of medium-Mn steel welded joint was 353 MPa at stress ratio of -1 and 10⁷ cycles. When obvious welding defects existed in the medium-Mn steel welded joint, the fatigue crack initiated at the microscopic defects. When no welding defects existed in the weld, the fatigue crack initiated at the fusion line of the sample surface. The surface of the fatigue crack propagation zone was rough, and obvious secondary cracks existed. There were a large number of uniform and fine dimples on the surface of the transient fracture area.