The invention discloses a water transparent primer for loose putty. The water transparent primer is composed of the following raw materials, by weight: 67.5-95 parts of one-component waterborne epoxy resin, 0.2-5 parts of wetting agent, 0.0375-1 part of defoaming agent, 0-1 part of preservative and 5-18 parts of water. The water transparent primer for loose putty obtained by the invention can well solve a problem that using common primer on the loose putty causes serious decrustation. In addition, the product uses water as a main carrier, so as to bring good social benefits in the perspectives of environmental protection and human health; therefore, the water transparent primer for loose putty is especially suitable to be used as an interior wall paint.