Abstract: The effects of laser power, welding speed, wire feeding speed and beam swing trajectory on the weld formation and defect tendency in narrow gap laser wire filling welding were studied by using 20 mm thick 10Ni5CrMoV high strength steel plate as the test material.The results show that crack and pore are the main welding defects.The dendrites on the crack fracture are arranged in bundles and the surface is smooth and round, which is typical solidification crack.Under the process parameters in this paper, with the increase of laser power, the depth to width ratio of the weld increases significantly, and the tendency of solidification crack increases first then decreases; when the welding speed increases to a certain value, the pores and cracks are significantly reduced; with the wire feeding speed increasing, the penetration of "finger" weld decreases, the waist tendency decreases, and the pores decrease.The beam oscillating pattern has a significant inhibitory effect on the generation of pores, but it cannot inhibit the generation of cracks.