A loop heat pipe with flat evaporator includes an evaporation section, a condensation section, and a transportation section connected between the evaporation section and the condensation section. The evaporation section includes a heat source, an enclosed containment structure, and a capillary structure. The enclosed containment structure is positionable on the heat source and forms an enclosed containment space which receives a working fluid and has a bottom in which a channel structure is formed and further forms a liquid inlet and a gas outlet in a circumferential wall thereof the container to respectively connect a liquid passage and a gas passage so that when the working fluid is heated by the heat source to become vapor, the vapor moves through the gas outlet and the gas passage to a condensing device provided in the condensation section where the vapor is cooled and converted back to the liquid form of the working fluid that is then guided through the liquid passage back to the enclosed containment space for next cycle.
