The existing fillet modeling algorithms are suitable for a single scene, and when modeling in complex areas, there are problems of low stability and poor modeling surface quality, which affects the design efficiency and overall quality of die surface. So it is necessary to study an efficient and stable fillet modeling algorithm to improve the design quality and shorten the development cycle. Therefore, a complex fillet modeling algorithm based on section curve rounding was proposed to achieve the stable creation and flexible editing of free fillet surface, and the algorithm converted the complex surface rounding into the section curve rounding, which significantly reduced the complexity of the algorithm. Then, through the section curve interference inspection algorithm, the self-intersection areas of section curve were searched and reconstructed to ensure the stability and quality of the constructed fillet. Furthermore, based on the custom object technology of NX platform, the fillet modeling function was developed, which realized the high efficient creation and stable updating of the fillet surface. The results of the actual automobile covering panel model test prove that the proposed algorithm is stable and reliable, with high editing efficiency and rich adaptation scenarios, which effectively improves the efficiency of designers and shortens the product development cycle.