Abstract: A company used TU1 oxygen free copper bars to manufacture electric vacuum devices and the copper bars bubbled on the surface in the process of packaging. The surface bubbling reasons were analyzed by means of macroscopic examination,metallographic examination,chemical composition analysis, TEM analysis and energy spectrum analysis. The results show that the TU1 oxygen free copper bars had subcutaneous shrinkage defect because of the incomplete tail resection in the process of extrusion, and the oxide inclusions in the subcutaneous shrinkage defect was the main reason for the surface bubbling of the oxygen free copper bars.