Based on a detailed study of compositional characteristics of fluid inclusions in major gold deposits along Machaoying faulted belt, the authors have summed up fluid geochemical characteristics and probed into compositions, sources and evolution of the fluids. It is held that the ore-forming fluids are of mixed geneses characterized by low salinity, weak alkalinity and relatively high degree of mineralization, with the ore-forming fluids being derived from deep sources at the early stage and mixed with large quantities of meteoric water at the late stage. The factors governing fluid evolution and the mechanisms controlling the migration and precipitation of gold and other ore-forming materials in fluids have been analyzed. The fluid activities seem to be the key factor for mineralization. The systematic study of ore-forming fluids helps to reveal in essence the metallogenic conditions and geneses of gold deposits in Machaoying faulted belt, and contributes to better understanding of gold metallogenic regularity and prognosis of ore deposits.