The tumble ratio and discharge coefficient of high tumble ratio intake ports with Mask airflow blocking structure were simulated by CFD three-dimensional simulation and the effects of Mask and its width and height on tumble ratio were emphatically discussed. The steady simulation of flow characteristics was conducted on eight high tumble intake ports without Mast and with Mask of 0.2mm, 0.5mm and 1mm width. AVL average tumble ratio was 3.0-3.5 and AVL average discharge coefficient was 0.25-0.30. Then the intake port with Mask of 1mm, 2mm, 3mm, 4mm and 5mm height were simulated and analyzed respectively. The results show that the tumble intensity increases significantly at small valve lift and the tumble ratio decreases slightly at large valve lift after using Mask. The larger tumble ratio produces at small valve lift when the smaller width and the larger height of Mask are used. AVL average tumble ratio increases by 6.4% and AVL average discharge coefficient decreases by 11.4% when the Mask height increases from 1 mm to 5 mm.