Objectives: Elucidating the mechanism and determining the time of fracturefilling in carbonate concretions in the Lower Cambrian Qiongzhusi Formation in the northern Sichuan of Southwestern China;Methods: Thin sections that were doubly polished and blue epoxyimpregnated were produced to determine lithological components, diagenetic phases and prepared for fluidinclusion work. The fluidinclusion measurement was employed for experimentation at Southwest Petroleum University, which involved the use of a THMSG600. Electron probe analysis was employed for experimentation at Southwest Petroleum University, which involved the use of a JXA8230. Samples for isotopic analysis were microdrilled from the cores. Stable isotopic (δ18O, δ13C) analyses of different periods fracturefilling were carried out at Southwest Petroleum University using the carbonate reaction method. Samples were reacted by the application of the Phosphoric acid bath method at 90℃, and the CO2 generated was examined through use of Elementar IsoPrime GC5. Results:The firstly micritic calcites filled in fractures which have dirty crystalsurface are null luminescent under CL, and the calcite filling fractures also exhibit negative values of δ13C and δ18O, respectively with an average of -4.26‰ and -7.69‰; hints that calcites may have been formed in early dehydration. The secondly fine to medium calcites filled in fractures which are orange luminescent under CL, and fluid inclusion analyses of twophase aqueous inclusions in calcites suggest that second fracturefilling occurred at temperatures with an average of 86.4℃. The negative values of δ13C and δ18O (respectively with an average of -3.15‰ and -7.41‰) indicates that calcites may form due to hydrocarbon generation by early mature source rocks. The thirdly coarse, blocky calcites filled which are null luminescent under CL, and fluid inclusion analyses suggest that calcites occurred at temperatures with an average of 96.6℃. The negative values of δ13C and δ18O (respectively with an average of -1.73‰ and -10.28‰) inferred that calcites may form due to uplift and depressurization in Caledonian tectonic movement. The barites are formed by sulfate reduction reaction in deep buried stage.