Abstract: Disclosed are a grouting material for modifying mudstone, a preparation method and an application thereof, belonging to the technical field of material science and geotechnical engineering. The grouting material for modifying mudstone includes the following raw materials: cement, water, superfine micronized powder, water reducer, silane, fiber, diatomite, urea-formaldehyde resin and waterborne polyurethane. The preparation method of the grouting material for modifying mudstone includes steps of: (1) weighing the raw materials in parts by weight, mixing water of 40% of a total amount of water with water reducer, superfine micronized powder, fiber and diatomite, stirring to obtain a material A; (2) adding silane, urea-formaldehyde resin, waterborne polyurethane and residual water into the material A, obtaining a material B after continuous stirring; and (3) adding cement into the material B, and uniformly stirring to obtain the grouting material for modifying mudstone.