Abstract: The welding test of 6.6 mm thick D406A ultra-high strength steel plate was carried out by using multi-layer narrow gap laser filler wire welding with beam oscillation, and the welded joint with high forming quality was obtained. The effects of laser beam oscillation and quenching+ low temperature tempering heat treatment on the microstructure and properties of the joint were analyzed. The results show that the transverse oscillation of laser beam can improve the width of heat deposition area and effectively prevent the poor fusion defects of inter layers and side walls. The microstructure of the fusion zone of the welded joint is mainly strip martensite, and the base metal zone is the weak zone of the joint. After heat treatment, the microstructure of fusion zone, heat affected zone and base metal zone of the joint is tempered martensite, and the weld zone is the weak area of the whole joint, the tensile strength of the joint is 1625.8 MPa, the average impact energy at room temperature is 28.74 J; the bending angle is 35°, which meets the industry requirements.