Abstract: The rotor deflection is an important part of steam turbine calculation. The rotor deflection curve can also provide a basis for adjusting the clearance during the installation and alignment process of the rotor. Firstly, a rotor calculation model was established. The Segmental integration method was used to analyze the calculation process of rotor support reaction force, bending moment, and deflection distribution. The C # language tool was applied to develop interface programs for the theoretical calculation process mentioned above, achieving fast and accurate calculation functions. Finally, select a rotor with equal cross-section, compared the program and theoretical calculation results, the error is within 0.2%.Select a rotor instance, compared the results of the program and finite element simulation, the error is within 4.5%.Verified the rationality of the program.