The Bainaimiao Cu-Au-Mo deposit is an important ore deposit in the middle section of the north margin of North China Block, and the mineralization characteristics of the Bainaimiao deposit show both porphyry alteration features, as well as the characteristics of late orogenesis transformation. Systematic micro-thermometry, laser Raman and chromatography analysis are carried out on fluid inclusions, which reflect the ore-forming fluid is middle-low temperature CO2 (CO)-H2O-CH4 (C2H2 C2H4)-NaCl-CaCl2 system, and fluid mixing and CO2 escaping are the main factors of mineralization. Reducing fluid may urge the vapor fluid carrying ore-forming elements such as Cu, Au migrating to distant Bainaimiao group, then, deposits along the foliation or fissures. The 3He/4He and 40Ar/36Ar values (3He/4He=0.06~0.71 Ra, and 40Ar/36Ar=375.5~1436.3, respectively) of the fluid inclusions in pyrites from the different mineralization phases in the Bainaiiao deposit suggest that the ore-forming fluid system is mixed by two end members, one is the high temperature deep-derived fluid congenetic with the porphyries generated by crust-mantle mixing; another is the low-temperature meteoric water which is rich in crustal radiogenic He with the component of atmospheric Ar. We consider that the Bainaimiao deposit belongs to the porphyry deposit that suffered the late orogenic transformation, and the deposit formed under the background of the paleo-Asian Ocean plate continued southward subduction.