For the inner wire joint parts in automobile brake pipeline, the boss structure which is the internal key part has the characteristics of small size and high size accuracy requirement. A six-die and six-punch cold heading processing method was adopted for production. Firstly, the orthogonal experiment of three factors and three levels were designed according to the key dimension factors affecting the boss forming. Secondly, Deform-3D finite element analysis software was used to analyze equivalent stress, equivalent strain and force distribution of die for the boss forming step in the orthogonal experiments, and the calculated deformation degrees of step 2-step 4 were 42.7%, 66.0% and 40.0%, respectively. At the same time, the affecting degrees of various factors on the boss forming was obtained as preformed boss depth > flange height > distance from upper end surface and top surface of preformed flange, and the optimal size combination was found under the conditions of full boss forming and minimum punch force, that is, the preformed boss depth is 9 mm, the flange height is 6 mm, and the distance from upper end surface and top surface of preformed flange is 11 mm. The study result provides a certain guidance for the cold heading of the similar boss parts in the future.