Abstract: The diagenesis of the Chang-3 and Chang 4+5 oil measures in the Baibao Oil Field,Changqing is treated on the basis of the integration of thin section analysis,electron microprobe scanning,vitrinite reflectance and organic matter maturity.The diagenetic stages comprise compaction,cementation,dissolution and hydrocarbon emplacement.Four diagenetic reservoir facies types and their planar distribution have been ascertained with the aid of the genetic artificial neural network.