The invention discloses a wall-mounted microwave oven fan fixing device. The fixing device comprises an exhaust fan and a fan motor which are arranged at the upper rear part of a mounting disk. The fan motor is arranged on the mounting disk by a motor support, the exhaust fan is arranged at the left side of the fan motor, and a cooling fan is arranged at the right side of the fan motor. The motor support is provided with two ribbed plates, and two connecting grooves are arranged at positions of a bottom face plate of the mounting plate corresponding to the two ribbed plates. The fixing device has the advantages of simple structure, easy positioning, convenient operation and firm connection, and the device overcomes the disadvantage that the fan can not operate normally due to heating deformation of the motor support.