A liquid-cooled heat dissipation system includes a heat absorber; a heat dissipating member; two connecting pipes connecting the heat absorber and the heat dissipating member; and a working fluid filled in the heat absorber, the heat dissipating member, and the connecting pipes. The working fluid is capable of circulating in the circuit. The working fluid includes a base fluid, a plurality of nanoparticles and a protective agent dispersed in the base fluid. A percentage by weight of the nanoparticles in the working fluid is in the range from 0.1% to 3%.