We analysis the paleofluid geochemical features of fractures from Yidi-2 Well，the discovery well of Cambrian shale gas. The forming environment of paleofluids and its indications to shale gas preservation of Shuijingtuo Formation are further discussed，as preservation conditions are key factors for shale gas enrichment in the middle Yangtze. The following results are obtained. The calcite veins above Qinjiamiao Formation lack of Fe2+, Mn2+ and δ13C values and δ18O values smaller than surrounding rocks mean the oxidation environment. Calcite veins δ13C lighter than surrounding rocks and pyrite δ34S closed to gypsum indicate they are productions of TSR. The calcite veins of Shuijingtuo Formation and Yanjiahe Formation formed in enclosed environment with δ13C and δ18O closed to surrounding rocks. SO42-, Ca2+, Mg2+ contents of vein inclusions decrease from Qinjiamiao Formation to upper and deeper layers, the lowest (rNa+/rCl-) value in Shuijingtuo Formation indicate that Qinjiamiao Formation is the main source of high-salinity brine and Shuijingtuo Formation is hardly affected by the external fluids. δD and δ18O also indicate the veins in Loushanguan Formation and Shipai Formation formed with meteoric water an TSR respectively. The preservation condition in Yichang area is generally good for shale gas, the vertical fractures were ways to shale gas losing. The gypsum cover, weak tectonic movement in later stage, veins plugging fracture, rapid deposition of Cretaceous have relation with good preservation condition.