Abstract： Based on the requirements from American Petroleum Institute (API) standards and a theory of pre-nesting for section steel, a calculation model of pre-nesting for composite beam-steel is given by the Visual Basic (VB) computer language. The software of purchase and pre-nesting is then developed, which is named BYMAX 1.0. The main functions can be summarized as below. The first part is to calculate the size and number of steel plates with a smart and high-speed process. And the second part is to check the results and to show the nesting pictures by calling AutoCAD. This part can guarantee the accuracy of the previously obtained results.