Abstract: The chemical composition analysis and elemental line scanning analysis of the root of thick plate HQ785T1 steel laser-arc hybrid welding joint filled with HS-70 were studied, the test results show that the element content of the weld is between the base metal and the welding wire, the element composition of the weld seam is closer to the base metal with the increase of the depth. The composition of the root weld is mainly composed of base metal, the proportion of the welding wire is small; The value of the impact toughness is lower than the upper part of the weld, the impact toughness of the weld root decreases with the increase of the blunt edge of the groove; The microstructure of the weld center of the root is granular bainite structure. With the increase of blunt edge size, the amount of carbide precipitation decreases, the microstructure is slightly coarser, and the brittleness increases.