The invention discloses a pneumatic valve actuator internally provided with a heat preservation device. The pneumatic valve actuator comprises a valve body, an actuator body, an air compressor, a controller, a ventilation mechanism and an actuating mechanism, the valve body is arranged under the actuator body, and the bottom end of the valve body is in surface contact with a working plane; the air compressor, the controller, the actuating mechanism and the ventilation mechanism are arranged in the actuator body, the air compressor is arranged at the upper end of the actuator body and fixed to the inner side wall of the actuator body, and the controller is arranged at the lower end of the actuator body and fixed to the inner side wall of the actuator body. One end of the ventilation mechanism is connected with the air compressor, the other end of the ventilation mechanism is connected with the actuating mechanism, the actuating mechanism is arranged at the lower end of the actuator body, and the end, away from the ventilation mechanism, of the actuating mechanism penetrates through the side wall of the actuator body and extends into the valve body. The air compressor, the controller and the ventilation mechanism are electrically connected.