The invention discloses a GNSS (Global Navigation Satellite System) sea surface geodetic height surveying buoy, comprising an A-frame, a floating ball, a GNSS antenna and an instrument cabin, wherein the instrument cabin is located at the center of the A-frame, the A-frame is connected with the floating ball, the GNSS antenna is fixed on a sealed hatch on the upper part of the instrument cabin, and an antenna cover is mounted on the GNSS antenna; the floating ball is a solid and light ball body, the center of the floating ball is provided with a through round hole, a support rod extended from a vertex angle of the A-frame penetrates through the round hole in the center of the floating ball, and the floating ball is fixed on the support rod of the A-frame; the instrument cabin is fixed on the A-frame, the top surface of the instrument cabin is provided with the sealed hatch, and a power supply, a GNSS receiver and an attitude sensor are arranged in the instrument cabin; the GNSS antenna adopts a choking coil antenna, and is connected with the GNSS receiver in the instrument cabin by a coaxial cable; a GNSS base station is utilized to perform dynamic relative positioning on the GNSS buoy, and an accurate sea surface geodetic height is acquired according to the height and the attitude of the antenna of the buoy.