The invention relates to a gas-liquid separation flash evaporation degassing tank which mainly comprises feed tower bodies, a scrubber and a horizontal liquid storage tank, wherein feed ports are formed at the tops of the feed tower bodies; the feed tower bodies are internally provided with feed distributors, gas-liquid separation sections, and tower trays; the feed distributors are arranged above the gas-liquid separation sections; the feed tower bodies are arranged at the top of the horizontal liquid storage tank, and communicated with the horizontal liquid storage tank; liquid outlets are formed at the bottom of the horizontal liquid storage tank; the scrubber is arranged at the top of the horizontal liquid storage tank, and communicated with the horizontal liquid storage tank; an exhaust outlet is formed in the scrubber; a drop settling section and a spray catcher are arranged in the scrubber; and the spray catcher is arranged above the drop settling section. With the adoption of the gas-liquid separation structural form, compared with the traditional gas-liquid separation degassing tower in the same specification, the height of the gas-liquid separation flash evaporation degassing tank is decreased by more than 2.5m, and the degassing tank has better degassing, anti-foaming and anti-flooding effects; and with the adoption of the horizontal liquid storage tank, the air-liquid separation is facilitated, and the gas-liquid separation flash evaporation degassing tank has an excellent degassing performance.