The invention discloses a wellhead connecting device of a high-pressure underground gas storage well. The device comprises a cylindrical body, an integrated connecting seal head and a seal ring, wherein the lower part of the cylindrical body is provided with a taper pipe thread; the upper part of the cylindrical body is provided with a fastening thread or is provided with the fastening thread and a seal groove; and the integrated connecting seal head is provided with a liquid discharge port, a fuel gas inlet and a fuel gas outlet. According to the invention, a thickened cylindrical connecting pipe is adopted as the body of the connecting device and the integrated connecting seal head, during installation, the lower part of the cylindrical connecting pipe can be placed in a cement base under the ground surface, and is convenient for anti-corrosion treatment for the upper part, thus the connecting device has the characteristics of simple and compact structure, good integrity, safety and reliability in use, long service life and the like, is convenient to mount and dismount, is easy to perform heat preservation, heating and anti-corrosion treatment on the connecting device in daily use, and is convenient to overhaul and maintain the gas storage well.