Abstract: Effective discrimination of produced-water source is an important measure to determine the multi-layer commingling production of coalbed methane (CBM), and the stable isotopes in water are key indicators of water source information. In the Upper Permian western Guizhou, multiple coal beds are developed, and the CBM exploitation is dominated by multi-layer commingling production in vertical wells. There is significant difference in productivity under various horizon assemblages, and the produced-water source is unable to be effectively discriminated. Accordingly, based on the periodical acquisition of produced-water samples from 11 CBM wells in Bide-Santang Basin, western Guizhou, isotopic geochemical test was conducted on 38 samples of produced water, mine water and surface water. In combination with production data of CBM wells, this study reveals the hydrogen and oxygen isotopic composition characteristics of produced water in the study area as well as the significance of water source discrimination. According to atmospheric precipitation line equation, the produced water of CBM well generally presents an obvious D drift characteristic for hydrogen and oxygen isotopic composition, of which the hydrogen and oxygen isotopes are heavy in the closed water with intense water-rock interaction. Typical high-yield and low-yield wells are distinguished. The low-yield wells are restricted by surface water interference, of which the produced water presents light hydrogen and oxygen isotopes and insignificant D drift, while high production wells are characterized by heavy isotopes and obvious D drift trend in produced water. Moreover, the parameter reflecting D drift degree is set, and this value is positively related to average daily gas yield while negatively related to average daily water yield. In combination with Cl^- and Na⁺ concentrations, the discrimination model of discharge-production water source is created based on the geochemical characteristics of produced water. Three kinds of water source, i.e., shallow groundwater, coal seam water and fracturing water, are distinguished, while high CBM production can only be achieved when the coal seam water is produced in gas wells. As easily interfered by shallow groundwater, the upper gas-bearing system in this region has poor drainage-production conditions and low compatibility with the mid-lower gas-bearing system. Thus, it is suggested to give priority in developing the mid-lower gas-bearing system.