Abstract: Yan'an formation Yan 10 member is one of the most important oil layers of Mesozoic Erathem in Ordos basin.By means of analyzing lithofacies-palaeogeography before Jurassic Yan'an formation deposition,the paleogeographic environment of control Yan'an formation Yan 10 reservoir distribution was summarized in Zhidan oil field.The deposition from Fuxian to Yan 10 period of middle and lower of Jurassic fills and levels up the palaeogeomorphology of early Jurassic.Under the physiognomy of the intermeshing distribution and hypsography of ancient land,kopje and channel,the sphenoid sand body was formed on the ramp region of paleohigh,and lithologic-structural trap was very easily formed with the late differential compaction,then reservoir was readily formed.Moreover,Jurassic Yan 10 reservoir has the characteristics of good reservoir and active edge-basal ground water,and it is favorable for development.