A 2D/3D transformation method used for computer aided garment design is presented in this paper. The method is based on spring-mass model. 2D to 3D and 3D to 2D transformations for cloth patterns can be implemented within the same model. In 2D to 3D transformation, 2D cloth patterns are located in their initial positions near the mannequin. Under the applying of sewing force, the cloth patterns are deformed and sewn together on the mannequin automatically. In 3D to 2D transformation, 3D cloth patterns are mapped on a given plane initially. Under the applying of elastic deformable forces, the initial mapped 2D cloth patterns will be deformed and the final shapes of the 2D cloth patterns can be obtained. In 2D/3D transformation for cloth patterns, collision detection is also considered.