Aiming at the problem of speed fluctuation caused by the hard dot arrangement of the automobile double cross shaft universal joint steering system,the layout of hard spot how to ensure universal constant velocity transmission is studied,and taking the double cross shaft universal joint transmission structural optimization of a car as example,by using ADAMS / view software,the parametric dynamics model of double cross shaft universal joint transmission mechanism is built.Taking the variable in structure as design variable,taking the interaxial angle between intermediate shaft and the input shaft,the output shaft is not less than 155° as constraint condition,taking the angular difference of interaxial angle between intermediate shaft and the driving,driven shaft as the optimization target,and setting the steering intermediate shaft phase angle,the best hard spot layout program of double cross shaft universal joint steering system is acquired,and the steering transmission without fluctuation.