The oxygen and carbon dioxide are available active gas and both are commonly applied in MAG welding,the amount of their addition has definite influence on the fatigue performance of austenitic stainless steel. Through pulsating tensile fatigue test and metallographic structure analysis,the fatigue performance of MAG welding butt joint of 06Cr19Ni10 steel with two different kinds of protective atmospheres is studied. The results show that the median fatigue strength of φ（Ar）95% +φ（CO,2,）5% is 300 MPa,the median fatigue strength of φ（Ar）97%+φ（O,2,）3% is 302.5 MPa. The fracture location of specimen mainly concentrates in the heat affected zone. The crack starter location is obvious in the crack initiation zone;the fatigue striations on the extending zone are clear;the final broken zone is the toughness dimple type of fracture;the matrixes of the microstructures of two types of welded joints are both austenitic,and there are δ ferrites distribute on the matrix.