The invention discloses an air inlet duct. The air inlet duct comprises an air inlet duct body, wherein the air inlet duct body comprises an air inlet part and a connecting part connected with the air inlet part; a first channel is arranged inside the air inlet part; a second channel is arranged inside the connecting part; the first channel and the second channel are arranged in a penetration manner; one side of the connecting part is provided with a connecting surface which tilts towards the axis of the air inlet duct body; and the connecting surface extends to the end part of the connecting part in an inclined manner from a joint of the connecting part and the air inlet part, so that the area of the cross section of the first channel is greater than that of the cross section of the second channel. According to the air inlet duct and the combustion system of the turbocharged gasoline engine provided by the invention, the connecting surface axially tilts towards the center of the air inlet duct body, so that extrusion effect on air flow is achieved to forcibly change the flow direction of the airflow, and air flow with a high tumble ratio is formed at the connecting surface of the connecting part, and therefore, the combustion efficiency of the engine can be improved. In this way, a part is not needed to be additionally arranged on the air inlet duct or an air cylinder cover, so that the structure is simple, and the manufacturing cost is greatly reduced.