Abstract: The PuKou Formation in Huaiyin depression is composed of cyclothemes of salt rocks,mudstones and shales,which formed saline-lake sedimentary assemblage of more than 1000 m thick.During the aggradation of PuKou formation。the Huaiyin area was a wide lake which consisted of alluvial fans,littoral facies, shallow-lake facies and semi-deep-water facies.The saline sediments were formed in the semi-deep-water saline lake.In this paper,based on the geologic,seismic,geochemical,and palaeobiogical data, the sedime ntation environment of PuKou Formation and the genesis of saline sediments a discussed. Nowadays, there a three viewpoints on the formation of saline substances: (1)the saline substances from the marine transgression, in association with arid or semi-arid climate,and precipitated as saline deposits.(2)in the high-mountain-deep-basin environments, the saline substances from the weathering and leaching rocks such as carbonates, gypsolytes or other salinastones.(3)the saline substances derived mainly from the deep sources which were evidently related with faults or volcanism of the tectonic zone.In this paper, the author agrees with the third point.The reason are as follows:①the sedimentary characteristics:the saline deposits mainly belong to sodium-sulfate-chloride type.The sediments are cyclothems of saline rocks,mudstones and shales. ②the depositional conditions:many faults developed in Huaiyin depression during the formation of the saline deposits.③the asymmetry of salinity.④the palaeontological characteristics.All above- mentioned proofs show that the salt in deep strata was the major source and the deep fractures were the oaths through which the salt substances entered into the depression.