A lot of potholes are observed in the lower reaches of the Yellow River. According to their geneses, the potholes may be divided into six types; (1) flow-erosion; (2) wind-erosion; (3) circular boulder moulding; (4) ice-pressing; (5) ice-melt-water-erosion; (6)air-discharging erosion. The potholes formed by flow erosion are greatly varied in size: the small ones have a diameter of ten-odd centimetres and a depth of a few centimetre-s; and the large ones have a diameter of a few metres and a depth about one metre. Wind-erosion potholes are commonly small in size with their diameters no more than twenty to thirty centimetres, and their depths gener-ally below ten centimetres, and their walls gently plunged like a pot or dish. The potholes formed by casting of circular boulders are small in size, with a diameter below ten to twenty centimetres and sharply plunged walls. The Potholes formed by ice pressing are also small, with diameters ranging from ten to about thirty centimetres and depths less than ten centimetres, and have a relatively simple form. The potholes formed by ice melt water erosion have very complicated forms and variable sizes. They assume either dish-like forms with gently tilted walls or cylinder forms with almost vertical walls and their diameters ranging from several centimetres to thirty-forty centimetres. Secondary structures may often be found on their edges, walls and bottoms. There are four formation mechanisms of the ice-melt-water-erosion potholes. The potholes formed by air discharging erosion also have very complicated forms, which are considerably round to nearly round or other complicated forms. Their walls are gently or steeply plunged, with diameters from several to several tens of centimetres and depths from several millimetres to twenty-thirty centimetres, and commonly associated with secondary structures on edges and walls. They appear individually or in groups or gather like honeycombs. This type of potholes have a very unusual genesis, which is mainly related to the discharging air trapped by the riverbed during the Yellow River's zero flow period.