The present invention relates to an aquaculture cage elevation adjusting device and an open sea gravity-type farming cage thereof. A water storage floating vessel and a water storage sinking vessel of said aquaculture cage elevation adjusting device form a communicating vessel by means of a communicating pipe. The water storage floating vessel and the water storage sinking vessel communicate by means of a first water pipe and a second water pipe. The first water pipe controls a switch by means of a solenoid. The water storage sinking vessel is provided therein with a submersible pump, which is connected to the second water pipe and may pump fresh water in the water storage sinking vessel to the water storage floating vessel by means of the submersible pump. A plurality of mooring cables of the open sea gravity-type farming cage are circumferentially distributed along the body of the cage. Each mooring cable corresponding to the open sea gravity-type farming cage is provided with the aquaculture cage elevation adjusting device. The water storage floating vessel of each aquaculture cage elevation adjusting device is provided on the mooring cable, and each mooring cable corresponding to the water storage sinking vessel is provided on the bottom of the body of the cage. The present invention guarantees the long-term reliability of aquaculture cage elevation adjustment and has a simple structure.
