Geyserite Cs-deposit, occurring in the sediment of high-temperature geothermal action, is the particular Cs-deposit in Tibet. They mainly distribute in the violent geothermal active regions. The fact that the geyserite Cs-deposit is discovered only in Tibet has relation with the modern tectogenetic movement of the Tibet plateau by all appearances. This paper studied the geochemical characteristic of Cs in geothermal fluid and geyserite, the correlation with some irons (including Rb, Cl, Li et al.). Based on the research of the geochemical activity of Cs, the paper sum up the enrichment process of Cs in geothermal activity: partial anatexis of crust conduced the preconcentrating of Cs; crystallizing, separation of magma resulted in the re-concentrating of Cs; large scale reaction of fliud-rock induced Cs more enrichment in fluid.