The invention relates to a low-pressure drop horizontal water-sealed tank. The tank comprises a horizontal tank body, a flue gas inlet pipe, a flue gas outlet pipe, a water-sealed cover, support shafts and a driving component. The flue gas inlet pipe and the flue gas outlet pipe are respectively arranged on the upper part and the lower part of the horizontal tank body. The upper end of the flue gas outlet pipe extends into the horizontal tank body and approaches the flue gas inlet pipe. The water-sealed cover is composed of two fan-shaped side plates and a curved shield plate connected with the circumference of the two fan-shaped side plates. The flue gas outlet pipe is located between the two fan-shaped side plates of the water-sealed cover. The two fan-shaped side plates are respectively arranged in the horizontal tank body, through the support shafts. The two support shafts are both arranged along the axis of the horizontal tank body. The fan-shaped side plates is fixedly connected with the support shafts. And one of the support shafts extends out through the end enclosure of the horizontal tank body and connected with the driving component in a transmitted mode. The water-sealed tank is of compact structure and low pressure drop, the intensity of pressure is low, the flue gas can directly enters the flue gas outlet from the flue gas inlet, which makes the resistance loss of the flue gas passing through the water-sealed tank is much more smaller.