Die-less spinning is a forming process to achieve cone shape parts. It is suitable for small batch production because of low costs and short development cycle. In order to increase the forming accuracy of the square section die-less spinning process, the roller path is designed and amended. Using a 5-axis CNC spinning machine, the square section cone is spun and its edge arc degree is calculated. Roller path amendment coefficient is proposed and deduced through the geometric relationship. Based on the experimental result in which the amendment coefficient is employed, the second amendment coefficient is deduced and used to perform another spinning experiment. By comparison of the section edge arc degrees of the workpiece obtained with and without using the amendment coefficients, it is found that the forming accuracy in experiments with the amendment is remarkably enhanced.