Abstract: In order to automatically obtain types and numbers of parts in vector engineering drawings, we propose an algorithm for recognizing symbols. At first, we define three common properties for each element and a relation descriptor between two elements. A two-layer structure is introduced to simplify the representation of symbols, which are traditionally represented by constraint-networks or trees. Then, symbols are recognized via matching relation descriptors and building two-layer structures of symbols. We also use the structure of quad-trees, a method of recognizing several types of symbols in one cycle, and a method of sorting relation descriptors to speed up symbol recognition. Experimental results illustrate that the proposed algorithm can recognize more types of symbols, requires less time, and is more robust under rotation and scaling transforms than the previous algorithms.