Objective To explore the mechanism and related factors of LVOT Velocity speed after AVR for severe AS. Methods 76 patients after AVR for severe AS were enrolled in this study. Divided into combined valvular disease group and pure AS group. And then divided the pure AS group into another two groups (I: Velocity of LVOT speed up; II: Velocity of LVOT is not speed up). Preoperative record LVEDD、thickness of IVS、whether combined aortic malformation、Velocity of LVOT、EF of LV and follow-up Echocardiography Postoperative. Results 2 of 26 patients’ LVOT Velocity speed up after AVR with combined valvular disease, 18 of 50 patients’ LVOT Velocity speed up after AVR with pure AS disease. For pure AS, there are statistically significant difference between the two groups of the LVEDD and the ratio between IVS thickness and LVEDD. For 18 patients whose LVOT Velocity speed up after AVR with pure AS disease, the velocity increases quickest in 1week post-operation and be back to normal about 6 months. Conclusion The incidence of LVOT Velocity speed up after AVR for severe AS is high. Velocity is increasing first and then decreasing. It will be back to normal about 6 months. Mostly are pure AS patients pre-operation. Related to LVEDD and the ratio between IVS thickness and LVEDD.