<p>The increase in frequency, severity, and destructiveness of droughts under global climate change, especially of megadroughts, has devastating impacts on agricultural production, economic development, and ecological protection. However, critical gaps remain in accurately identifying and quantifying megadroughts, which significantly impede effective preparedness, timely response strategies, and long-term mitigation efforts. Therefore, it is imperative to develop a robust method for identifying megadroughts in order to improve management strategies and enhance predictive capabilities for mitigating their severe impacts. Here, the standardized moisture anomaly index (SZI) was leveraged to monitor droughts in Shaanxi Province, China. Then, drought characteristics, namely duration (<i>D</i>), severity (<i>S</i>), and intensity (<i>I</i>), were extracted using the three-threshold run theory. Accordingly, the drought-affected area (<i>A</i>) was accurately quantified. The copula function was applied to analyze the three-dimensional joint return period of the <i>D</i>-<i>S</i>-<i>A</i> relationship. An identification method for megadroughts was developed, based on the functional relationship between the joint return periods and drought loss rate. The identification criteria for megadroughts were listed as follows: the drought characteristic values corresponding to the joint return period (<i>T</i>_<i>or</i>) were <i>D</i>, or <i>S</i> or <i>A</i> exceeding 12.5 months, or 8.5, or 21 × 10⁴ km², respectively; and for the co-occurrence return period (<i>T</i>_<i>and</i>), the criteria for <i>D</i>, <i>S</i>, and <i>A</i> were greater than 16.5 months, 5, and 20 × 10⁴ km², respectively. For the period 1961–2022 in Shaanxi Province, the <i>T</i>_<i>or</i>-based and <i>T</i>_<i>and</i>-based criteria identified seven and one megadroughts, respectively. These findings provide an effective reference for future identification and early warning of megadroughts.</p>