The invention relates to a silicic acid mud interior wall decorating material and a preparation method thereof. The silicic acid mud interior wall decorating material mainly comprises diatomite, sepiolite, kaolin, sierozem, coarse whiting, wollastonite, white cement, silica sand, talcum powder, nanometer titanium dioxide, ethylene-vinyl acetate copolymer, cellulose ether, aluminium-magnesium silicate, easily dispersed fiber, inorganic pigments and has the functions of humidity control and air purification. The preparation method comprises the following steps of: firstly acidizing the diatomite, the sepiolite and the kaolin, removing harmful ingredients in the diatomite, the sepiolite and the kaolin, improving the activation property of the material, then filtering, washing, drying and crushing, and finally adding the diatomite, the sepiolite and the kaolin and the other components to a dry powder blender for uniformly stirring. When being used, water is added to powder, so that the powder is prepared into paste or emulsion; the silicic acid mud interior wall decorating material is suitable for roll coating, spray finishing, blade coating and the like in interior wall decoration and has the functions of indoor humidity adjustment, peculiar smell elimination, removal of harmful gases such as formaldehyde and toluene in air and lasting environmental protection and simultaneously has the characteristics of rich color, strong sense of texture and environmental friendliness.