Abstract: The effects of hase material thickness, surface condition and interlayer material on AZ31B magnesium alloy ultrasonic welding were investigated. The result showed the material near the welding contact would be torn in the test of shear strength, and surface bonding strength could achieve about 3-10 MPa. The effect of surface condition on the surface binding strength of the magnesium alloy strip welding was relatively small for ultrasonic welding could break and clean the welding surface. The additive temperature was not needed on ultrasonic welding. And the welding area temperature promotion was inverse proportion to the welding material thickness. The results also showed the choice of interlayer material was useful to the Mg/Mg interface ultrasonic welding.