Abstract: The Chenjiaba deposit is a new Cu-Pb-Zn polymetallic deposit discovered in Mianxian-Lueyang-Yang Pingguan triangle area, Shaanxi Province. Based on the geochemical comparison between trace elements and rare earth elements in ore and geological bodies, the ore-forming fluid characteristics and metallogenic mechanism of this deposit have been studied. The result shows that the ore in this deposit is rich in LREE, the Th/La, Nb/La and Hf/Sm ratios are all less than 1, respectively, indicting the geochemical feature of ore-forming fluid mainly enriched in Cl element. The ore has similar REE distribution curve, trace element cobweb diagram and element content with the silicified dolomite in ore-bearing horizon, suggesting that the ore formed by syngenetic sedimentary mineralization. The ore has negative Ce anomalies and positive Eu anomalies, which is similar to those of seafloor hydrothermal fluids and their sediments, indicating that the ore formed in a reducing environment. In the process of mineralization, the mixture of magmatic fluid, hot brine and sea water makes it more favorable for mineralization. Therefore, it is considered that the ore-forming fluid has the geochemical characteristics of the magmatic fluid mixed with hot brine and seawater. The fluid mixing action and the water rock interaction are important mechanisms for the enrichment and precipitation of Cu, Pb and Zn ore-forming elements.