Abstract: A new concept-welding technology margin is proposed in this paper.Welding technology margin means the degree to welding technology assures that the welded joints reach the quality standard of products of structures under the specified welding conditions (including welding methods,welding materials, welding parameters and structure types,etc.). This new concept is developed on the basis of weldability concept,which tightly integrated the welding technology with the quality standard of the product.Moreover,factors affecting the welding technology margin are discussed.The definition of an index for welding technology margin and the approach to the welding technology evaluation are put forward,and the application of welding technology margin in welding quality assurance is discussed.