There are plants on all the earthen sites located in the eastern Inner Mongolia. Plants are both good and harmful for earthen sites, so it is necessary to maxize the benefit and minimize the damage when using plant for protecting the earthen sites. The Sites of Yingchanglu State Capital, Xanadu and the Upper Capital of the Liao Dynasty were selected for field investigation to study the effects of plant coverage and plant root distribution on earthen sites. The results showed that the tops of the sites are covered with low - height herbaceous plants, mainly Leymus chinensis, Agropyron cristatum, Festuca rubra, Iris lactea, and Japanese Inula flower, and the coverage is within the range of 30% - 60%. The plants play an important role in protecting the sites against damages caused by rainfall and have little effect on the sites' overall landscape. Conclusion was drawn that plants can be applied to protect earthen sites that have plants, suffer serious rain erosion and cannot be satisfactorily protected by other existing methods.