A welding assembly for a liquid-injection hole of a secondary battery, including a top cover of a case, a liquid-injection hole, a sealing cover-plate and a stress release structure, wherein the liquid-injection hole is disposed in the top cover and includes a assembling recess and a through-hole arranged sequentially from top to bottom of the top cover, the assembling recess and the through-hole present a stepped transition and the radial dimension of the assembling recess is larger than that of the through-hole. The sealing cover-plate is accommodated in the assembling recess and the stress release structure is provided at one or both sides of the welding portion and capable of releasing stress from the welding portion. The welding assembly provides a stress release structure nearby the welding portion, and when the welding portion is full-strength welded, the stress-release structure can effectively release stress nearby the welding seam.