Established precise three-dimension model of spur gear based on hob-shaving process with virtual manufacturing approach. Carried out dynamic simulation analysis based on corner contact. Obtained the dynamic stress variation law of the gear under impact loads. The simulation results shows that the position of the maximum dynamic stress of the root of tooth under different condition appears in the both sides symmetrically, that the dynamic stress was bigger than the ISO Standard theoretic static strength under impact loads, and that the position of the maximum dynamic stress is on the high side of the dangerous section determined by ISO Standard, that the dynamic stress caused by the engaging-in impact was the maximum under different condition, and that the shorter the impact time is, the larger the dynamic stress is.