Abstract: The fluid inclusions of the metamorphic peak time fo r the Archaean granulite series in the Taipingzhai-Lozishan district, eastern H ebei Province were first found in sillimanite. According to their shapes and occurrences, these inclusions ca n be subdivided into three types. The earliest type is the isolated inclus i ons and inclusions in clusters with negative hexogonal, prismatic crystal forms . They are very rare and characterized by parallelism of their elongated direct ion with c-axis of sillimanite; The second type is the inclusions with irregula r shapes. They have no spatial relation to cleavage and (00 1) parting of host mineral; The third type is most common. The inclusions are usually square or rectangular. They occur along healed (001) parting perpendicular to c-axis of sillimanite, and were entraped in the later stage of the metamorphic peak time. As a whole , the compositions of fluids in above-mentioned three types are very similer. All they are chara cterized by:①rich in carbonic materials, with XCO2+CH4≈0.64～0.93; ② low in wate r , with XH2O≈0～0.22, which coincides well with activity of H2O ( 0.04～0.31) and mole percent of water (XH2O≈0.03～0.22) based on thermodyna mic calcula tion from equilibrium assemblage of peak metamorphism; ③with XH2S,SO 2 <0.10～0.21 in some cases; ④very low content of anions in halogenic solution (mostly 0.12～0.61mol/L). These inclusions have also been found in garnet an d quartz, but in the latter case, the inclusious are characterized by abundant two-phase H2O-C O2 chemistry, with XH2O >0.25～0.33. They were probably formed in the further late regressive stag e under the low PT condition. 　　The homogenization temperature of CO2 in fluid inclusions of peak stage ranges from -28℃ to -22℃ in most samples. The corresponding density is 0.96～1.06g /c m3, and total fluid pressure (Pf) is 0.60～0. 70GPa. This value is about 0.1～0.3GPa lower than the confining pressure of r ocks ( Pl) estimated by various geobarometers. The temperature of this stage is es timated at 780℃～790℃. Based on the XH2O, XCO2 and XCH4 relationship of fluid inclusions, together with diagnoti c assemblage of peak stage, the oxygen fugacity is calculated as log fO2=-17～-15. 　　All features of peak-stage fluids are rather homogeneous in space within a give n a rea, and values of aH2O are similar in associated rocks of differe n t lithology. These evidences together with regional geology and characteristics of protolith rocks suggest that predominant amout of CO2 in fluids might be o f de ep source and related to underplating of mafic magmas from the mantle and their cry stallization. The proposed mechanism is analogous to concept of carbonic metamo rphism.