Abstract: This paper proposed a vectorization method based on the run length coding for recognition of engineering drawings. We studied the aspects of the small bend line correction problem as well as the combining and extending algorithm of the vectorization line segments. At the same time, image morphology analysis method was also used in the research, which ensured the information integrity and graphic testability when directly using the original scanning image of the engineering drawings. The achievements have been used for automatical recognition and calculation of architecture engineering drawings.