Integrated analysis of petrography, isotopic geochemistry, fluid inclusions has shown that the Upper Sinian Dengying saddle dolomite from Well Lin-1 is relative with hydrothermal activity in origin. The saddle dolomite commonly coexists with quartz and bitumen. The saddle dolomite shows rather low values of δ18O(‰) and δ13C(‰) and very high values of 87Sr/86Sr, which is significantly different to those from the surrounding rock around Dengying Formation. Primary fluid inclusions in the saddle dolomite comprise of gaseous CO2, CH4 andN2 and liquidusH2O and CO2, Primary homogenization temperature of the inclusions is at 270-320 ℃ which is obviously higher than the maximum burial temperature of this area. It is suggested that the Dengying dolostone reservoir was altered by hydrothermal dissolution and hydrocarbon accumulation happened later in it.