The lower first member of Shahejie Formation (Sha 1 Sub-member) in the Qijiawu area in Huahua depression is dominated by carbonate reservoirs. Lithochemical analysis of 10 cores, carbon and oxygen isotopic and trace element compositions show that the content of SiO₂, Al₂O₃ and CaO are relatively high, while the content of MgO varies with the difference of lithology. Detailed studies of petrochemical composition, C and O isotopic analysis, and trace elements contents establish the geochemical basis for reconstructing ancient geographical environment of Sha 1 sub-member rock facies and predicting favorable reserves zones in the studying area.