For the analysis of bolt-nut joints, the finite element method has been used by several investigators. However, they had difficulties in applying the finite element method to bolt-nut joints with fastened plate. Although the analysis of elastic bodies in contact is not so easy, it is important to solve such problem as bolt-nut joints. Conclusions derived from this study are as follows : A numerical method to analyse bolt-nut joints with many contact surfaces is developed here. The flank load ratio to axial tension can be analysed if there are pitch and flank angle modifications. Also this method makes it possible to analyse the elastic-plastic problems of bolt-nut joints.