The research of stable carbon and oxygen isotope of Carbonate of lake sediments, is one of the most effective indices to reconstruct paleoclimatic and paleoenvironmental information. Sedimentary carbonate consists mainly of allochthonous carbonates produced by surface runoff and authigenic carbonates produced by inorganic precipitation. However, the authigenic carbonate has the paleoclimatic and paleoenvironmental meaning. Consequently, distinguishing the source of carbonate is the basis and premise for the research of sedimentary carbonates. This paper utilized various methods to prove that the carbonate in Lake Chenghai,Yunnan Province was authigenic, which provided the basis for the research of sedimentary carbonates. Lake Chenghai provides an ideal lacustrine setting for research of stable carbon and oxygen isotope to reconstruct paleoclimate, and the future research will be deserved.