The invention relates to a multi-scale capillary core flat plate loop heat pipe type heat-dissipation device, and belongs to the technical field of phase transition heat dissipation. The heat-dissipation device comprises an evaporating part, a condensing part, a compensating cavity, a gas phase pipeline and a liquid phase pipeline, wherein the gas phase pipeline is connected with the evaporating part and the condensing part, and the liquid phase pipeline is connected with the condensing part and the compensating cavity; a base plate of the evaporating part is in a flat plate shape, metal powder is sintered to form two layers of multi-scale capillary cores at the upper surface of the base plate, and a steam channel is constructed between the two layers of capillary cores; a layer of water absorption cotton tightly covers a second layer of capillary cores and is taken as a third layer of capillary cores, and the three layers of capillary cores form a multi-scale structure. By utilizing the multiple layers of multi-scale capillary cores and the constructed steam channel, the problem of the contradictoriness between the vapor-liquid flow resistance and the capillary suction force is solved, the starting temperature of a loop heat pipe is lowered, the high heating flux bearing capacity of the heat-dissipation device is improved, and the instability in heat transfer is reduced; the multi-scale capillary core flat plate loop heat pipe type heat-dissipation device has the advantages of high cooling capacity, large heat flux bearing capacity, low starting temperature, small temperature fluctuation, good antigravity performance and long transmission distance.