Calcareous incrustation in the sand-mud interface of lenticular sandbody is the production of interacting process of mudstone (hydrocarbon source rock), liquid (oil, gas and water) and sandstone (reservoir rock) in petroliferous basins. The interaction of hydrocarbon source rocks and formation water produces organic acid that can dissolve minerals, especially carbonate minerals. Hydrocarbon liquid which is produced in hydrocarbon source rock and formation water, transfer to the lenticular sandbody in the vicinity under the effect of impetus. The organic acid bearing carbonates also migrates with them. The liquid which is produced after the interaction of hydrocarbon source rocks and aqueous solution will enter a new reservoir rock. In the new physicochemical environment, it will react with the reservoir rock again. The direct result of interaction of liquid and reservoir rock is the precipitation of calcite and dolomite, which will occupy some pore space of the source rocks and create cements, then the calcareous incrustation will be formed. The carbonate cements, mainly consisting of ferroan calcite and ankerite, are telogenetic cements. The content of carbonate cements in lenticular sandbody has a negative correlation with porosity, permeability and hydrocarbon saturation of lenticular sandbody. The existence of calcareous incrustation causes the change of pore structure: the primary pores are infilled by carbonate cements, the secondary pores being developed are intercrystal and intracrystal micropore; mercury-injection curves are steep, displacement pressure and median pressure are high; pore interconnections are too small and sediments are poorly sorted. Refined analysis on the anatomization of six sand-bed groups in 2 939～3 003 m of Well Niu 35 of the middle part of Member 3 of Shahejie Formation of Paleogene in the Dongying Sag indicates that calcareous incrustation in sand-mud interface is an important factor to control the hydrocarbon accumulation of lenticular sandbody.