Some embodiments of the present disclosure provide a water retaining structure and a humidifier with the water retaining structure. The water retaining structure is disposed on a bottom surface of a water tank assembly. The water retaining structure and the water tank assembly are split. The water retaining structure includes a mist collecting portion and a water retaining portion. The mist collecting portion is formed into a mist collecting space. The mist collecting space communicates with a mist outlet tube in the water tank assembly. The water retaining portion is configured to collect water flowing down from the mist outlet tube. The water retaining structure and the water tank assembly are split so that the bottom surface of the water tank assembly is configured as a flat surface, or a height of a structure disposed on the bottom surface is reduced.