Abstract: The characteristics of fluid inclusions in Dayingzi gold deposit, Hebei Province are as follows. The fluid belongs to Na⁺-K⁺-Ca²⁺-Mg²⁺-F^--Cl^- type. The salinity is low-medium degree. Ore-forming temperature is about 280℃ with pressure 74.7 MPa, which indicates the ore-forming depth is about 3 km, thus the deposit belongs to low-middle temperature sy stem. The fluido riginates from mixed resource, i.e., former magmatic water mixed with the later subterranean halogmenic water.