A full-section heading machine cutter head device with the variable cutting diameter comprises a cutter head body, a turntable, expanding parts, extending-retracting oil cylinders, connecting rods, cutting teeth, oil cylinder displacement sensors and a turntable angle sensor. The cutter head body is used as supporting parts; the turntable is installed at the center of the cutter head body and connected with the extending-retracting oil cylinders and the connecting rods; the connecting rods are connected with the expanding parts and the turntables; the expanding parts are arranged in sliding channels of the cutter head body; the oil cylinders and the connecting rods are arranged on the turntable; the cutting teeth are arranged on the cutter head body and the expanding parts; the other ends of the three oil cylinders are evenly distributed on the cutter head body; the oil cylinder displacement sensors are installed inside the oil cylinders; and the turntable angle sensor is installed on the cutter head body. An electric control system of the full-section heading machine cutter head device can precisely calculate the excavation diameter of a cutter head by measuring the displacement amount of the oil cylinders with the displacement sensors or the rotating angle of the turntable with the angle sensor, and can manipulate extending and retracting of the oil cylinders to enable the diameter of the cutter head to meet the requirement, and the full-section heading machine cutter head device is applied to the technical field of coal mine roadways and tunnel projects.