The analytical data of carbon and oxygen stable isotopic composition of carbonate rocks from saline lakes on Qinghai-Xizang plateau indicate that carbonate sediments in saline lakes are rich in carbon-13 and oxygen-18. Most of the values coincide with values of marine carbonates,with relatively high Z value. So when using carbon and oxygen stable isotopic values or Keith and Weber’s Z value as the discrimination oriteria for sedimentary environments, one must consider the characteristics of saline lakes so as to avoid incorrect results.