To address the limitation that the spatiotemporal dynamics are rarely considered in the determination of thresholds for groundwater ecological level, this study proposes the principles, concepts, and determination methods for dynamic thresholds for groundwater ecological level, and applies them to the Ningxia Yellow River Diversion Irrigation Oasis. By means of theoretical calculation of capillary water rise height, field experiment observation and analysis, vegetation survey, and lake water balance analysis, the groundwater ecological levels corresponding to salinization, vegetation, and lakes were determined respectively, and then the dynamic thresholds for groundwater ecological levels in different periods were obtained. The results show that: the groundwater ecological level thresholds corresponding to salinization control, vegetation growth, and lake ecological maintenance in the Ningxia Yellow River Diversion Irrigation Oasis are 1.5~1.8,2.5~3.5, and 2.7~3.5 m, respectively; dynamic thresholds for groundwater ecological level exhibit obvious spatiotemporal dynamics. Specifically, the dynamic thresholds for groundwater ecological level from January to March and from October to December are composed of the thresholds for salinization control and lake ecological maintenance, with the upper limit of 1.5~1.8 m and the lower limit of 2.7~3.5 m; the thresholds from April to September consist of those for salinization control, vegetation growth, and lake ecological maintenance, with the upper limit of 1.5~1.8 m and the lower limit of 2.5~3.5 m. The optimal and safest ranges of dynamic thresholds for groundwater ecological level are 1.8~2.7 m for the periods of January to March and October to December, and 1.8~2.5 m for the period of April to September.