This paper emphasizes on the analysis of fracture mechanical characteristics of 3-Point Bending Specimen suffering driving force. By analyzing the structural characteristics of the 3-Point Bending Specimen, the equivalent mathematical model mass-damping-spring system has been formulated. The variation of parameters method is then used to solve the corresponding second order differential equation and find the general analytical formula for the Dynamic Stress Intensity Factor. This analytical formula for Dynamic Stress Intensity Factor will be useful for the further researches and practical engineering design and applications in fracture mechanical field