Slitting shears are used not only for shearing strip but also for shearing plate with thickness up to 40 mm in metallurgical enterprise.Hence, the calculation of the force and energy parameters during shearing process is significant for designer and user.Shearing force P is the most important parameter, However, the existing calculation methods for P are basically semiexperimental formulas which generally have a reasonless case that the shearing force P is up to infinity when biting angle a_0 approaches to zero. The calculating formula of shearing force P isderived in this paper based on shearing features and fracture principle.The results show that thecalculated changing pattern of shearing force P with overlap S of disks coincide with the testing result and the reasonless case is eliminated.