The invention relates to a dragging, dewatering and shrinkaging method and device of floating macroalgae. The dragging, dewatering and shrinkaging device is arranged on a seaweed-harvesting vessel to harvest the macroalgae floating on the lake or near sea surface and dewater and shrink the harvested algae. The device of the invention comprises a flexible floating trawl, a water pump, a conveying device and an extruding, dewatering and shrinkaging device, wherein the flexible floating trawl is used to block and harvest the algae; the water pump is used to suck the algae in the flexible floating trawl onto the vessel; the conveying device is used to separate the algae which is sucked by the water pump onto the vessel, from water; and the extruding, dewatering and shrinkaging device is used to extrude, dewater and shrink the algae which is separated by the conveying device.