In order to improve the quality and productivity of software, the software structure which is deeply related to them, is observed in this paper. Firstly, the problems of software structure analysis and design of current methods are examined. Then, the HOQ (house of quality) concept of the QFD (quality function deployment) is extended as a tool for software description based on the similarity between HOQ in quality design and engineering drawing in product design. By applying Simon's idea of system's near decomposability, the quantitative structuralization method is proposed based on the QMT3 (quantification method of type 3). Furthermore, the features of this method are clarified by comparison with the current methods. Finally, the effectiveness of the method for software structure analysis and design is verified by an application. Therefore, the method can help successfully for assurance of software quality.