The invention discloses a multi-layer coextrusion device and an application method thereof. The multi-layer coextrusion device comprises a machine head, an active paying-off machine, a conductor paying-off disc, a dance wheel, a heater, a coextrusion machine head, a constant-temperature water tank, a traction device and a winding disc. The coextrusion machine head comprises a composite module, a shell, a front gland and a rear gland. The composite module comprises a die core supporting sleeve, a wire inlet positioning module, an inner conductor layer module, a PTC layer module and an insulation layer module. The PTC layer module comprises a PCT wrapping die and a sizing die. The position, at the PTC layer module, of the die core supporting sleeve is provided with a first annular boss. ThePCT wrapping die is provided with a first linkage part to be matched with the first annular boss, and the PCT wrapping die is in sliding connection with the sizing die. According to the multi-layer coextrusion device and the application method thereof, through the arrangement of a first gear set and a second gear set, reverse rotation of the PTC layer module and the insulation layer module is achieved, and fixation between a PTC heating body layer and a composite insulation layer is tighter.