The invention discloses an air supply system of a long tunnel. The air supply system aims to solve the problem that the air supply volume and the air supply position in a traditional tunnel are not adjustable. According to the key points of the technical scheme, the air supply system of the long tunnel comprises a tunnel body, and an arch-shaped channel is arranged in the tunnel body; preformed holes are formed in the positions, near the channel, of the tunnel body in the length direction, and air outlets communicating with the channel are formed in the side walls of the preformed holes; a wind supply mechanism is disposed at the position, near the side wall of the channel, in the tunnel body, and the wind supply mechanism includes an air duct assembly disposed in the preformed holes; theend portion of the air duct assembly is connected with a draught fan, and the air duct assembly is provided with adjusting mechanisms for adjusting air volume of the air duct assembly; and the numberof the preformed holes is five and the preformed holes are equally distributed along the curved faces of the channel. According to the air supply system of the long tunnel, the adjustment of the air supply volume and the air supply position in the channel can be realized, and the application is more flexible.