Abstract: A loop thermosyphon cooling device includes an evaporator, a condenser and a communication assembly. The evaporator includes a heat conducting element and evaporation pipes, and the heat conducting element has through holes, and each evaporation pipe is passed and positioned into each respective through hole. The condenser includes a condensation pipe. The communication assembly includes a first barrel and a second barrel, and both ends of each evaporation pipe are communicated with the first and second barrels, and both ends of the condensation pipe are communicated with the first and second barrels, so that the evaporation pipe, condensation pipe, first barrel and second barrel jointly define a loop. A communication assembly is coupled between the evaporation pipe and the condensation pipe, and the quantity of evaporation pipes and condensation pipes can be increased or decreased as needed, and the thermosyphon cooling device is compact and high heat dissipation efficiency.