Abstract: Based on the fact that there exist regular coefficient relationship and substitution relationship between the dimensions of different parts of the flat oval tube,a method for designing the coefficient of the groove of the standard flat oval tube is deduced with relevant mathematical manipulation. As a result,the pass deformation coefficient λ_i is obtained,and it is applicable to any groove of the standard flat oval tube. And then,the relationship between coefficient λ_i and R,the curvature radius of the standard flat oval tube end is directly used to design the deformation dimensions of different parts of each pass for the oval tube. Thanks to this method,the design program can be simplified,and furthermore,the design efficiency is improved.