Based on the basic structure and operation function of engine throttle, according to the actual structure of a throttle, a 3-dimensional simulation of the transient airflow during the rotation of the throttle from the closed position to the fully open position is realized by using CFD together with the moving mesh technology and the user-defined program. The influence of the throttle movement on the airflow process is studied. The velocity field, pressure field, and flow noise field are analyzed at different angles of throttle rotation. The numerical simulation results show that at the beginning period of the throttle rotation, the vortex appears in the flow field behind the throttle, and the drop of the air pressure between the upstream and downstream position of the throttle is sharp. In addition, the results show that the flow noise field appears near the top dead center and bottom dead center of the throttle, and the maximum value of the acoustic power appears when the throttle opening is near 40 degrees. With the increase of the throttle rotation angle, the vortex gradually weakens, the difference of the air pressure between the two sides of the throttle becomes small, the flow noise first increases and then decreases, and the maximum value of the acoustic power appears all the time at the downstream position of the throttle, and its positions are gradually moved away from the axes of the throttle. When the throttle is fully opened, the velocity field, pressure field and flow noise field gradually tend to stabilize.