The invention discloses a slender shaft one-cutter turning method. The slender shaft one-cutter turning method is characterized by comprising the following steps: materials are prepared; conventional heat treatment and straightening treatment are performed; a center hole is drilled by a conventional method, and a workpiece clamping end is pre-turned; a lathe with a follow rest structure is adopted, a support head of the follow rest is a cuboid structure, and an orthographic projection of a support surface of the support head in the axis direction of the support head is rectangular; cutter selection: a tool cutting edge angle of a turning tool is 90-93 degrees, a tool minor cutting edge angle of the turning tool is 7-9 degrees, and a rake angle is 20-27 degrees; cutter installation: a cutter nose is lower than the axis by 0.1 mm; clamping method: an axial thermal extension gap more than 1 mm is reserved by a screw nut; and the turning is finished by a conventional method. The slender shaft one-cutter turning method is high in effect, can turn an excircle part body of a workpiece slender shaft by one cutter, only needs about 20 minutes to turn a slender shaft about 2 meter, improves the effect by about 30 times, is high in processing precision and stable and reliable in quality, saves the processing cost, and can save the processing cost by above 70% through batch production.