Abstract: An approximate developing method has been proposed for the complicated curvedsurface which is usually non-developable. Take a sphere-body as an illustration. It isfirstly divided imaginarily into several hypothetical quadrangles whose contour are definedby following the short routes of geodesic parallel lines. A mathematical model couldthen be established through theoretical operations. By the mathematical model the prac-tical drawings can be obtained by using the computer. The latter may be used by theworkmen for the torch cutting; directly the method has been checked and compared withthe conventional practice and is found that it would give the best approximation thanthose ever taken and consequently it will offer the optimum saving of the constructingmaterials.