A typical Mesozoic (Tertiary) synsedimentary system of evaporate and mudrock occurs in the middle and lower parts of the 4th Member of Shahejie Formation in the Dongying sag, East China. To investigate mineral elements, carbon isotope, and hydrocarbon generation of synsedimentary evaporate and mudstone, an intense sampling for saline section was conducted in two deep wells (well Haoke1 and well Fengshen2) in the Dongying Sag. The results show remarkable response differences, characterized with low contents in Al, Mn and Ba, high in Na, Ca and Mg, and abnormally high in Sr; and a distinct response of distribution of feature element ratios, low V/Ni, and（Fe+Al）/(Ca+Mg), and high Sr/Ba, Fe/Mn and Sr/Ca. The distribution of mineral elements displays clear discretion and fluctuation; inorganic elements is depleted in evaporate but enriched in neighboring mudstone (except sodium, which is also enriched evaporate). δ13C values of different group compositions and nalkane composition range from -28‰ to -21‰ and -18‰ to -32‰, respectively. δ13C factionation between compositions of organic group is relatively low (less than -2‰), while nalkane shows a distinct δ13C change in C17 and C18. The δ13C value of residual hydrocarbon from source rock was increased by thermal evolution and TSR reaction. The synsedimentary system of evaporates and mudstone has potential capacity of hydrocarbon generation and expulsion. The organic matter dominates decayed mud and can be divided into type Ⅰ and type Ⅱ1The original potential capacity of hydrocarbon generation and expulsion can reach 40 mg/g and 20 mg/g, and the efficiency of hydrocarbon expulsion attained 60%. But they both show intense heterogeneity in both plane and cross section. The content and maturity of the mudstone and generation and expulsion of hydrocarbon are higher than those of evaporate. In addition, high thermal evolution is likely to result in decreasing of generation and expulsion of residue hydrocarbon.