<p>Precipitation isotopic (δ¹⁸O and δD) diagnostic is fundamental for tracing regional hydrological cycles, but this owns great challenges in data-deficient areas. Especially, over the Qinghai–Tibet Plateau, the harsh environment and/or the unavailable data result in limited sites and short-term data series, which hinders the precipitation isotopic diagnostics, especially the tempo-spatial analysis and the establishment of the local meteoric water line (LMWL). Taking Qaidam Basin as an example, only the discontinuous δ¹⁸O observation data (δD data are not publicly available) is available for only one Delingha site. It proposes to employ the simulated data of atmospheric general circulation models (AGCMs) with global and long-period coverage to comprehensively analyze the precipitation isotopic characteristics, with the supplementary of the other three sourced data. The good agreement of the results among different sourced data verifies the applicability of this method, indicating its potential application to other areas, but with calibration of existing hydro-meteorological data with AGCMs in advance and uncertainty assessment. The precipitation isotopes show less spatial differences across the Qaidam Basin, while the deuterium excess (d-excess) increases eastward. The precipitation isotopes and d-excess show seasonal variations, while there is no consistency in their annual variations. The LMWL across the Qaidam Basin is established and the slope increases eastward. These findings help better understand the precipitation isotopic characteristics in the Qaidam Basin.</p>