China Great wall is one of the most important world cultural heritages. Investigation on preparation and rainfall erosion of rammed earth in Great Wall sites is significant to avoid occurrence of geological disasters in the sites. In this study, an efficient preparation method for rammed earth of Shanhaiguan Great Wall site is proposed using clay, lime and pre-gelatinized starch. A series of direct shear tests are conducted on rammed earth samples with different lime and pre-gelatinized starch contents, relationship between peak shear strength and lime and pre-gelatinized starch contents is analyzed. According to comparison results of mechanical parameters (cohesion and internal friction angle) between in-suit and prepared rammed earth samples, combinations of pre-gelatinized starch and lime contents to prepare rammed earth are recommended. Moreover, a preparation method is proposed for developing a geopolymer-based protecting coating (GPC) using geopolymer, nano-calcium carbonate (nano-CaCO3), and silane coupling agent. By conducting a series of raindrop splash tests and rainfall erosion tests, effects of activator modulus (Ms), nano-CaCO3 content, and silane coupling agent content on mass loss ratio of rammed earth samples during test are discussed. In addition, using response surface method, response surface tests are conducted and optimal ratios of GPC (Ms of 2.63, nano-CaCO3 content of 2.41%, and silane coupling agent content of 1.28%) are determined. Under optimal ratios of GPC, mass loss ratio of rammed earth sample in raindrop splash test is 1.64%, erosion residual ratio of rammed earth sample in rainfall erosion test is 91.61%, which contributes to that GPC improves the strength and water stability of rammed earth surface. The results of this study could be useful for earthen site protection of Shanhaiguan Great Wall against rainfall erosion.