Abstract: This paper shows that there is no diffusing action of atoms in cold welding.This conclusion was drawn from a great deal of measuring experiments in the diffusing action of atoms at the interface of cold and other hot-pressure welded joints by using advanced technique such as neutron activation,S.E.M.,spectral analysis,etc.It points out that atomic diffusion is not a must action in all welding and that cold welding is a type of intergranular metallic bonding.Suceessful butt cold welding has been made between the metals of incoherent lattice and non-solublc liquidoid and non-soluble solidoid.So in theory and practice the scope of weldable metals is broadened.The diffusing action of atoms at the interface of various cold welded joints after heat-treatment was also measured and its rule of diffusion found.