Taking the typical three units multi-rotor tandem shafting in petrochemical industry as an example, the method of finite element was used to analyse the torsional vibration characteristic of multi-rotor tandem shafting. By the Dyrobes and the idea of brick pattern, the typical model, that was three units multi-rotor tandem shafting entity model was established, then the Cambell drawing, critical speed and vibration mode of multi-rotor tandem shafting were analysed. Results show that the torsional resonance critical speed point avoid effectively ±10% of the working speed, and the intersections of double frequency and all the critical speeds are beyond the scope of work speed safety margin, which comply with the API engineering standards. The modeling is simple and intuitive, together, the research provide theoretical and technical support for the design of multi-rotor tandem shafting and safe operation of the unit shaft rotor.