Soil based composite wall material was prepared with orthogonal experimental design, and lime and fly ash were used as the stabilizers. The effect of stabilizer content and moisture content on hygrothermal comprehensive property of soil based composite wall material was studied by multivariate nonlinear regression, then the optimal preparation parameters for soil based composite wall material were obtained. The results indicate that hygrothermal comprehensive property is significantly influenced by stabilizer content and moisture content. Significance order is moisture content＞fly ash content＞lime content＞blank factor. The optimal preparation parameters were proposed that lime content is 624%, fly ash content is 893%, moisture content is 1357%. Thermal conductivity and equilibrium moisture content of optimal soil based composite wall material were 0721W/(m·K) and 7645%, respectively. Tested results show that optimal program has the acceptable compressive strength and water resistance. The composition and microstructure analysis results indicated that hydration products of fly ash enhance the matrix of optimal soil based composite wall material to be a more dense structural system under the effect of alkaline excitation.