The invention relates to a well-sinking and water-purifying method for a river bank multilayer structure, wherein a water purifying building is composed of a cutting edge, a well wall, a bottom plate water-resisting layer, flared opening bases, flared opening water inlet tanks containing bosses, a pump set platform, a chlorine disinfection chamber, a power distribution duty room, a laboratory, a shallow type grit chamber. In an improved water purifying building, the cutting edge is sunk while earth is cut, when the cutting edge is sunk to a projected depth, the well wall is reinforced by a tons support, so that the well ring is not sunk, and the flared opening water inlet tanks containing the bosses can be conveniently installed. Prefabricated flared opening bases are arranged below the cutting edge, the flared opening water inlet tanks containing the bosses in a shape that an outer part is big and an inner part is small are installed between the flared opening bases, and then sand gravels outside a well are prevented from flocking into the well. A sunk well is not sunk due to the flared opening bases and a certain water depth is kept in the well and water can be easily pumped. In an installation process of the flared opening water inlet tanks containing the bosses, because the flared opening bases are provided with the bosses which are concave-convex coupled with the cutting edge, the flared opening bases can be conveniently installed, and workload is reduced and a sunk well is not inclined.