The invention discloses a large transmission tower suction type barrel-shaped foundation structure and a construction method. The structure comprises at least one suction type barrel-shaped foundation sunk in a river network swamp foundation by using vacuum negative pressure in a barrel, wherein a barrel top platform is cast at the upper part of the suction type barrel-shaped foundation; a flange plate is embedded on the upper surface of the barrel top platform; and at least one connecting end bottom flange at the lower part of a transmission tower and the flange plate are connected through a bolt to form a whole. The construction method comprises the following steps: a) the prefabricated suction type barrel-shaped foundation is carried to the scene to form a sealed barrel-shaped structure; b) after the installation is finished, such lifting equipment as a crane is used for lifting the suction type barrel-shaped foundation to a designed tower position on an appointed soft soil layer; and a suction barrel sinks by a certain depth under the condition of self weight beforehand; c) water and air in the barrel are sucked out from an exhaust hole in the upper part of a cover of the suction barrel by exhaust vacuum equipment, and negative pressure is formed in the barrel; and d) after the barrel foundation reaches a preset elevation, the negative pressure in the barrel is released to finish the construction of the barrel foundation.