The disclosure relates to a flow-rate adjustment component and a liquid cooling device. The flow-rate adjustment component is configured to be in contact with a plurality fins, and every two adjacent fins are spaced by a passageway. The flow-rate adjustment component includes a covering portion and at least one blocking portion. The covering portion has at least one through slot. The covering portion is in contact with the fins to cover the passageways. The through slot is connected to the passageways. The at least one blocking portion is to block one end of at least one of the passageways.