The utility model discloses an underground tubing-casing annulus pressure-reducing device which comprises an oil tube collar, a central tube, an adjusting compression ring, a seal ring, a spring, an annular check valve, an annular valve seat and an outer working barrel; the annular valve seat, the annular check valve, the spring, the seal ring and the adjusting compression ring are arranged inside the outer working barrel and outside the central tube in sequence; and the outer working barrel is fixed outside the central tube through welding. The utility model can reduce the tubing-casing annulus pressure of an oil well and improve the efficiency of an oil pumping system of the oil well, has strong reliability and can be widely applied to oil production.