Based on the modal analysis theory on vibration problems,a simplified model was established based on the PRO / E,for engine crankshaft of QT800- 6 material,to analyze the dynamic behavior and obtain effect of inherent frequency and vibration mode. The model analysis was done with ANSYS,obtaining the foregoing 8 orders of the non-zero frequency of the free modal and the constraint modal,which were then compared. Furthermore,by viewing the modal shape of the constraint modal,reasonable suggestions were propos...