The common hot stamping defects were analyzed. The basic flow of hot stamping defects on-line detection and key technology of the detection system were introduced, including the judgment of hot stamping defects, analysis of connected component with Blob algorithm, and determining the number of connected area, the information such as size, area and position. Hot stamping defects were classified successfully according to the features of connected area parameter. On-line detection of hot stamping defects was realized.