Abstract：The Budunhua Cu deposit is a porphyry-hydrothermal vein type composite deposit in the middle-south part of the Da Hinggan Mountains. The deposit consists of the southern Jinjiling porphyry Cu ore block and northern Kongqueshan hydrothermal vein-type Cu ore block. Based on a detailed analysis of geological characteristics and a study of hydrogen, oxygen, sulfur, and lead isotopes in hydrothermal minerals, this paper has discussed the origin of ore-forming fluid and materials and genesis of the Budunhua deposit. Hydrogen and oxygen isotope analyses indicate that the ore-forming fluid in the early ore-forming stage in Jinjiling and Kongqueshan ore blocks was mainly magmatic water, whereas that in the late ore-formaing stage was probably a mixed fluid of magmatic and meteoric water. Sulfur isotope analyses show that the Jinjiling ore block is relatively rich in 34S, with sulfur isotope composition of ore-forming fluid being +2.54~+2.60‰, while the Kongqueshan ore block is relatively depleted in 34S, with sulfur isotope composition of ore-forming fluid being -1.84~-1.71‰. The sulfur isotope composition of the two ore blocks suggest a deep-seated source, and the lead isotope results display crust-mantle mixing characteristics closely related to magmatism. With the regional geological evolution history of the middle-south part of the Da Hinggan Mountains as a premise, the mineralization of the Jinjiling and the Kongqueshan Cu ore blocks in the Budunhua Cu deposit should be mainly related to fluid mixing which led to the precipitation of metal sulfides.