The invention discloses a plugging permeability-preventing agent, which is prepared from the following raw materials in percentage by weight: 25% of caustic soda, 6% of sodium methyl silicate, 10% of quartz powder, 10% of gypsum and 50% of water. The preparation method of the plugging permeability-preventing agent comprises the following steps: firstly, adding water into the caustic soda for uniformly mixing and stirring, slowly adding the sodium methyl silicate, the quartz powder and the gypsum in the stirring process for uniformly stirring, and filtering waste residues to obtain a finished product. The plugging permeability-preventing agent of the invention is suitable for various concrete buildings such as roofs, oil depots, water towers, water channels, washing rooms and the like, canenable the gaps of cement mortar concrete to be compact, has the effects of preventing water and permeability, and simultaneously can improve the compressive strength and the tensile strength of the cement mortar concrete. Because the plugging permeability-preventing agent is ventilated, layer surfaces can not be expanded, deformed, weathered and peeled off and can be bonded together again to perform the action of plugging.