An air guide box includes a box body. The box body includes a first wall and a second wall disposed opposite to each other. The first wall has an air inlet. Air outlets are respectively disposed between corresponding edges of the first and second walls. The second wall is recessed toward the first wall, and a portion of the second wall corresponding to the air inlet is a largest recessed position. From the largest recessed position to the air outlets, the second wall is gradually inclined in a direction away from the first wall, so that an inner surface of the second wall facing the first wall forms guiding slopes respectively form the largest recessed position to the edges of the first and second walls.