The invention provides a horizontal liquefied gas sweetening tank. The horizontal liquefied gas sweetening tank comprises a tank body, an extraction unit and a separation unit, wherein the extractionunit comprises a feed assembly, an extraction component and a buffer tube which are connected sequentially, and a liquefied gas inlet as well as an alkali liquor inlet provided with a feed nozzle is formed in the feed assembly; the separation unit comprises an overflow plate, a coalescence plate and a baffle plate which are arranged sequentially in the material flow direction, the overflow plate is fixed at the bottom of the tank body, the coalescence plate is fixed at the top of the tank body, and the baffle plate is arranged in the middle of the tank body. The treatment capacity of a liquefied gas sweetening system can be improved by adopting the horizontal liquefied gas sweetening tanks in parallel connection or series connection under the condition that the original liquefied gas sweetening process is not changed much, and the horizontal liquefied gas sweetening tank has the characteristics that assembling is simple, piping is convenient and the like.