Abstract: As an important method, lead isotopic research not only is used for tracing ore material origin and calculating Pb model age, but also for applications to geochemical exploration and evaluation of deposits. Deep prospecting for Dashui gold deposit is the predominant task after exploration and development for 20 years. Geochemical exploration by Pb isotopes is applied in the Dashui gold deposit of Maqu County, Gansu Province, along the typical No.70 and 72 exploration lines, based on previous studies of the Pb isotopes. There are 78 Pb isotopic samples both rocks and ores collected for analysis and prediction for the mineralized depth. Based on the regional geochemical background, the cut-off V2 value of mineralization is established in a range of 22.42~34.36, Along the No.70 and 72 exploration line at the 3450m elevation, the V2 values are 49.11 and 64.83 respectively. Pb isotope forecast indicate that the cut-off depth of mineralization at No.70 to 72 and westward mineralized district is from 3000m to 3100m. Thus there is 400~500m great exploration potential in the depth, which is the focus of future mining exploration and deep exploration work should be strengthened.