The invention discloses waterborne impregnated resin, waterborne polyurethane superfine fiber synthetic leather and a preparation method of thewaterborne polyurethane superfine fiber synthetic leather. The waterborne impregnated resin is prepared from components in parts by weight as follows: 100 parts of a waterborne polyurethane emulsion, 5-30 parts of a water-soluble polymer, 0-100 parts of deionized water, 0.1-1 part of a wetting agent and 0-3 parts of a thickener. The preparation method of thewaterborne polyurethane superfine fiber synthetic leather comprises the following steps: sea-island non-woven fabric is impregnated in the waterborne impregnated resin and dried, and impregnated base cloth is obtained and fed into toluene for decrement; primary base cloth is obtained after washing and drying and is treated, and the waterborne polyurethane superfine fiber synthetic leather can be obtained. Environmental pollution is reduced greatly, part of soluble polymer granules are introduced, the release effect between fibers and resin is enhanced, and the obtained synthetic leather has a densercell structure.