The present disclosure relates to a cooling device for a power battery system, a power battery system for a vehicle comprising the cooling device, and a vehicle. The cooling device is disposed at a bottom of the power battery system and includes a chamber defined by a casing. The chamber includes: a first region where a liquid cooling plate assembly is disposed; and a second region sealingly separated from the first region and accommodating a piping system for coolant communication. The liquid cooling plate assembly extends from a bottom of the first region to a bottom of the second region, and the piping system is in fluid communication with a flow passage of the liquid cooling plate assembly. In the cooling device of the present disclosure, the piping system is all disposed outside the battery system. Thus, battery cells or high-voltage devices inside the battery system would not be affected even if the coolant leaks at the piping system, which greatly improves safety of the battery system.