The invention relates to a cationic concrete mud inhibiting agent and a preparation method thereof. The cationic concrete mud inhibiting agent consists of a phosphorous-containing or nitrogen-containing organic cation polymer solution and inorganic salt. The preparation method thereof comprises the following steps: (1) adding unsaturated carboxylate and epoxy alkyl halide in a reaction container, then adding a catalyst and a polymerization inhibitor, and reacting to obtain a first-step reaction product; (2) adding hydrochloric acid to the first-step reaction product to adjust the pH value to be 3-5, then slowly adding a quaternary phosphorus or quaternary ammonium solution, and reacting to obtain a second-step reaction product; (3) dissolving the second-step reaction product in water, adding an initiator for polymerization reaction, adding inorganic salt after the reaction is ended, and uniformly mixing to obtain the cationic concrete mud inhibiting agent. The mud inhibiting agent can preferentially adsorb clay mud with negative electric charges, an encapsulated shielding layer is formed on the surface of the clay mud, the electric charges among clay layers are exchanged, and the adsorption of extra water reducing agent is inhibited, so that the mixing amount of the concrete extra water reducing agent can be greatly reduced, and the concrete fluidity and the fluidity maintaining capability are improved.