Abstract: The Dongfengbeishan molybdenum deposit is located in northeastern Tianbaoshan ore concentration area in Yanbian Prefecture, Northeast China. Almost all discovered orebodies are controlled by faults and fractures in biotite quartz diorite, and characterized by veins and veinlets. The deposit experienced three metallogenic stages, namely quartz-molybdenite stage, quartz-polymetallic sulfide stage and quartz-calcite stage. Fluid inclusions in ore-bearing quartz veins can be classified into liquid-rich phase, gas-rich phase, daughter mineral-bearing three-phase and minor CO2-bearing three-phase occasional pure CO2 inclusions. Fluid boiling occurred during ore-forming evolution and might have played a very important role in metal elements precipitation. Besides H2O vapor, the gas phase in different types of inclusions, analyzed by Laser Raman Spectrum, also contains small amounts of CO2 and CH4, which indicates that the ore-forming fluid belongs to the H2O-NaCl±CO2±CH4 magmatic fluid system with medium-high temperature and medium-high salinity. The discovered vein molybdenum orebodies in the Dongfengbeishan molybdenum deposit resulted from the porphyry molybdenum mineralization, which implies that the metallogenic porphyry intrusion should have occurred under the biotite quartz diorite. The veinlet disseminated molybdenum mineralization has important guiding implications for further theoretical research and geological prospecting.