Through building “surface-molecule” interfacial adsorption structure model, the physical and the chemical absorptions of (001) interface and (010) interface of KDP crystal are studied by using molecular dynamics and density functional theory method, and the effect of temperature on physical absorption behavior is investigated. The result indicates that the absorption process and the growth habit of KDP surface are dominated by the chemical absorption, and the binding energy on (001) surface is 2.86 times that on (010) surface of KDP crystal. Near the saturation temperature, the binding energy between [H2PO4]- anion and crystal surface presents obviously an oscillation characteristic with the temperature varying, and the solution becomes unstable with the formation of anion clusters. With temperature decreasing from 323 K to 308 K, the binding energy of H2O decreases in general, but the binding energy of KDP molecular increases obviously, which indicates the dehydration process results from the competitive absorption between H2O and [H2PO4]-. The results obtained are of significance in identifying the surface kinetics process and developing more sophisticated crystal growth theories.