The invention discloses an automatic electrolytic cell liquid level control device which comprises a subsurface tank, a gas source, a pipeline system, a height sensor and a control system. The pipeline system comprises a gas inlet pipe, a gas exhaust pipe, a connecting pipe, an automatic reducing valve, an electric gas inlet regulating valve and an electric gas exhaust regulating valve. The gas inlet pipe communicates with the gas source. The gas exhaust pipe enables the gas inlet pipe to communicate with the outside. The connecting piece is connected between the gas inlet pipe and the gas exhaust pipe and communicates with the gas inlet pipe and the subsurface tank. The automatic reducing valve is installed on the gas inlet pipe. The electric gas inlet regulating valve is installed on the gas inlet pipe. The inlet end of the electric gas inlet regulating valve is connected with the outlet end of the automatic reducing valve. The electric gas exhaust regulating valve is installed on the gas exhaust pipe. The control system is connected with the electric gas inlet regulating valve, the electric gas exhaust regulating valve and the height sensor. The height of an electrolyte is adjusted by controlling the valve opening of the electric gas inlet regulating valve and the electric gas exhaust regulating valve. In this way, labor is saved, and the electrolyte is made to be in a stable state, so that the productivity of an electrolytic cell is improved.