Aiming at the problems of large deformation and poor quality consistency in the traditional machining process of slender shaft, the machining method of vertical double tool turning slender shaft is proposed。 The dynamic cutting force and deformation analysis in the vertical single tool and double tool turning process of slender shaft are carried out with the help of finite element software. The cutting force stability and work piece deformation of single tool and double tool turning slender shaft with the same cutting parameters are compared. The results show that double tool turning can effectively shorten the time when the cutting force enters the stable stage, and the bending deformation of slender shaft caused by double tool turning is only 6.6% of that caused by single tool turning. Vertical double tool turning can effectively reduce the bending deformation in the machining process of slender shaft, which provides a basis for high-speed cutting of slender shaft.