Applying the methods of atomic force, electron and optical microscopy the authors have studied the structure evolution at an intermediate stage of cold drawing at Ø1,3→Ø1,2 mm transition of superconducting Nb+47 % Ti alloy-based cable; the latter is used in magnetic system of the International Thermonuclear Experimental Reactor. The aim of the research is to analyze the influence of cold drawing deformation on the structure of multifilamentary Nb-Ti alloy-based superconductor. The authors have studied the microstructure, phase composition and their influence on properties of superconducting alloy Nb-Ti after cold drawing and intermediate annealing. The areas of plastic strain localization in spots of superconductor breaks were found out. The change of form and chemical composition of Nb-Ti fibers was detected in a defect-free region and in cable break zone. The authors determined the diffusion Nb barrier around Nb-Ti fibers in copper matrix. The laws identified should be taken into account when developing the cold drawing deformation technique to obtain the superconducting cores of the desired size.