Abstract: In the friction stir lap welding（FSLW） of aluminum/steel materials, continuous intermetallic compound（IMC）layer hinders the diffusion of elements and the metallurgical bonding of interface, which restricts the further improvement of the joint mechanical property. Taking 6061 aluminum alloy and 301L steel as the object, ultrasonic vibration was introduced into the FSLW process to increase strong plastic flow at the side of aluminum material, which inhibits excessive growth of IMCs, thereby improving the joint strength. The results show that with assisted ultrasonic, the average thickness of the continuous IMC layer at the FSLW joint interface is reduced from 10 μm to 6 μm, and the tensile load of the joint is increased by 27.9%.