The knowledge database of ready-to-wear included the clothing knowledge required in the process from design to manufacture. It is to carry on management and storage of the original trivial clothing knowledge, achieve rapid information access, delivery and response. People hope garment fit their body better, but now garment is produced in bulk. The challenges the company faces is to achieve intelligent pattern making and pattern individuation based on the knowledge database of ready-to-wear.to improve the production efficiency. In this paper, the relation among the different data in the knowledge database of ready-to-wear are studied. The key is how to achieve transforming the human body data, style and craft data to the pattern plate data, and ascertain the constraint relation between body measurement data and pattern plate data. Man’s shirt is taken as an example in this paper. The conversion function and the fitting curve of the back armhole are obtained through analysis of the pattern plate data in order to provide the foundation for achieving the transformation from data information to pattern sketch.