The effect of the inorganic modified admixture on strength, water resistance and humidity controlling performance of the sepiolite clay as humidity controlling materials was tested experimentally. The sepiolite humidity controlling materials with good strength, water resistance was researched by XRD, and the humidity controlling mechanism of the materials was investigated based on the microstructure analysis of SEM and the absorption/desorption theory of materials. The results show that when the content(by mass) of inorganic modified admixture is 15%25%, the compressive strength, softening coefficient, maximum equilibrium moisture content and the maximum absorption and desorption rate of the material at 60 days are 10.312.8MPa, 0.560.73, 18.3%21.5%, 0.0640.075kg/（kg·d） and 0.0440.050kg/（kg·d） respectively, which indicates that the materials have excellent comprehensive performance. The modified admixture reacts with SiO2 , Al2O3 and MgO in sepiolite to generate new products such as Ca·1.7MgO·3SiO4, Ca3Mg(SiO4)2, 2CaO·Al2O3·SiO2 and 2Ca2SiO3·CaCO3, and α C2S and γ C2S in modified admixture, The new products react with water to produce C S H gel, which is the main cause that makes the sepiolite humidity controlling material gain the excellent strength and water resistance. The surface physical and chemical adsorption, and the capillary effect of sepiolite clay on the water molecules in the air are the main causes that the sepiolite humidity controlling material has excellent humidity controlling performance.