A liquid-cooling heat dissipating device for dissipating heat by a casing includes a casing having a liquid flow channel and a heat dissipating fin, both integrally formed on a wall of the casing. The casing includes a panel having a cold connector and a hot connector. The cold connector is connected to a water tank and the hot connector is connected to the liquid flow channel. Another end of the connectors are connected to a water-cooling connector through a pipeline, and the water-cooling connector is installed at a heat source, such that the pipeline sends heated liquid to the liquid flow channel on the wall of the casing, and the heat dissipating fin on the casing dissipates the heat to the outside, and the cooled liquid is returned to the water tank and sent to the water-cooling connector on the heat source by the pipeline for repeated cycles.