Abstract: In this paper, the bound water adsorption in different depth of loess taken from Gansu Zhengning was determined by Isothermal Adsorption Method. The influence of bound water on the related parameters of loess was discussed. The results show that the water content of loess adsorption bound water mainly ranges from 5% to 7%.By comparing the absorption content of bound water and loess grain size analysis results, the results show that with the increasing of the fine-grained soil content, the loess tends to have a higher content of bound water, and particles content has the most significant influence on the bound water. Loess samples with higher bound water adsorption content tend to have higher liquid limit and plasticity index, and which indicates the fine-grained soil has stronger adsorption ability, thicker water film, and stronger plastic. Loess samples with high bound water content have a high natural water content, indicating a stronger natural water retention ability. In addition, the combination of loess has a certain effect on the determination of specific gravity, the proportion of bottle method in water and kerosene solution in the maximum error of up to 2.7%.Loess itself contains a combination of water content has the influence of the specific gravity, the greater the water content of the loess, the ratio of the actual value of the Loess measured relative to the actual value of the deviation is greater.