The invention relates to a method for processing a deep hole of a sleeve of a steam turbine by using a stepped reamer, and relates to a processing method for a deep hole of a sleeve. The method solves the problems that the sleeve has high possibility of deviation and vibration, the cutting elimination is difficult, the processed surface can be scratched and a cutter has high possibility of tipping when the deep hole of the sleeve of the existing steam turbine is processed. The method comprises the following steps: 1, discharging; 2, roughly turning an inner hole, an outer circle and both end surfaces of the sleeve for the first time; 3, quenching the sleeve; 4, roughly turning the inner hole, the outer circle and the both end surfaces of the sleeve for the second time; 5, tempering the sleeve; 6, finely turning the inner hole, the outer circle and the both end surfaces of the sleeve; 7, processing the inner hole of the sleeve on a lathe by using the stepped reamer; 8, grinding the inner hole of the sleeve; 9, drawing a hole line on the processing position of a radial hole; 10, drilling the radial hole; 11, milling the radial hole; 12, nitriding; 13, finely grinding the inner hole of the sleeve; 14, finely grinding the outer circle of the sleeve to complete the process of the deep hole of the sleeve of the steam turbine. The method is used for processing the deep hole of the sleeve of the steam turbine.