The selection of materials for reinforcement and protection of earthen archaeological sites located in humid environment has been a big problem in China for a long time. Currently, there are no standard procedures to follow. The Tanshishan Site in Fujian in southeast China is a typical coastal region earthen archaeological site in a humid environment. During the process of site protection in recent years, four kinds of reinforcement materials have been used according to the various base compositions. After a great deal of indoor and local field testing, it is found that long chain alkyl alkoxysiloxane, polysilicic acid ethyl ester mixture which contains oxygen group and sodium silicate and siloxane copolymer are good reinforcing agents and are effective in the humid environment of the Tanshishan site. This is a beneficial attempt and exploration for protection development of archaeological sites under humid environment in China.