The invention discloses a cleaning compound for a water closet and a preparation method thereof. The cleaning compound for the water closet comprises the following raw materials by weight: 1.6 to 3.1% of a cleaning agent, 1.8 to 4.4% of a shaping agent, 0.1 to 0.5% of a pH value conditioning agent, 0.5 to 1.5% of a coloring agent, 1.5 to 2.5% of sodium carbonate and 0.5 to 1.5% of a sustained-release agent, with the balance being anhydrous sodium sulfate. The cleaning compound for the water closet allows the inner wall of the water closet to maintain clean and be free of scale formation for a long time; through adoption of a reasonable formula, slow release of effective components is guaranteed, so the water closet can be cleaned, the longest service life of the water closet is guaranteed, and waste is avoided; and the cleaning compound is economical and practical and has a stable pH value, so early and later cleaning effect of the cleaning compound is maintained unchanged.