It is the stress intensity factor of crack tip on crankshaft of internal combustion engine that is the basis for calculating crack growth and residual life. Firstly,this paper using ADAMS software on the connecting rod system of crankshaft,analyzed the dynamics of rigid flexible coupling,draw that the fourth crank make maximum load. So in other same boundary conditions,the most prone elliptical crack is the direction of 45 DEG angle with the shaft shoulder,in the transition fillet of the fourth crank pin and Shaft Shoulder The load of the dynamic analysis calculation is regarded as the main force to calculate the intensity factor near the crack tip. Draw the trend of intensity factor with the crack depth changes under the different long and short axis ratio a / c. Under the condition of in considering the crack depth and the crack’s long and short axis ratio’s influence then fitting the expressions of shape factor of EQ4 H type internal combustion engine crankshaft. Laid the foundation for the followup work of fracture mechanics for this type internal combustion engine.