The invention discloses a gas drilling shaft drain system and a gas lifting optimization method. The gas drilling shaft drain system is characterized in that a first liquid flow meter is arranged on adownstream of a drilling pump; a pressure sensor is arranged on a downstream pipeline of the first liquid flow meter; a gas injection pipeline of a gas device communicates with a pipeline between thepressure sensor and the first liquid flow meter; the gas flow meter is arranged on an outlet of the gas device; and a second liquid flow meter is arranged on a pipeline between a liquid-gas separatorand a mud tank. The gas lifting drain method includes pure gas lifting and pulse gas injection lifting. The beneficial effects of the invention are that the liquid flow meters, a gas flow meter and adata processing control system can accurately calculate the amount of gas and liquid injected into a shaft during a drain process of the gas drilling shaft and the amount of liquid discharged from the shaft; and a data processing system can predict a flowing state in the shaft in real time, can perform prediction and determination, can predict and correct the gas discharge amount and the drillingliquid discharge amount in real time in a gas lifting drain process, can optimize control of the gas device and the drilling pump, and can control automatic completion of the gas lifting process.