Abstract: Aimed to get scientific "water stage-duration-frequency" (S, D, F) thresholds for wetland formation, the theory and method to determine wetland (S, D, F) thresholds were analyzed based on the related principles of pedology, plant ecology, system theory, geographic system theory, and inversion theory, etc. The result suggested that: ① Under normal circumstances, the S threshold for hydric soil formation and hydrophyte development should be determined in terms of the thickness of capillary fringe and the depth of the major portion of hydrophyte root zone in upper wetland boundary respectively; in lower wetland boundary, the S threshold should be determined at the maximum depth to which submerged plants normally grow; in a given year, the D threshold could only be inverted in stage hydrograph in terms of the altitude of wetland soil boundary or vegetation boundary; for stable wetland soil boundary or stable wetland vegetation boundary, the D threshold should only take the average value of the years, but for fluctuant wetland vegetation boundary, its D threshold is a constant. ② Under abnormal circumstances, the (S, D, F) thresholds of wetlands should refer to the (S, D, F) thresholds of wetlands "under normal circumstances" which belong to the same HGM regional subclass. ③ To test whether (S, D, F) thresholds is scientific, wetland hydrological boundary determined by the (S, D, F) thresholds must be coupled with wetland soil boundary or wetland vegetation boundary. The construction of the theory and method makes it possible for wetland scientists to study (S, D, F) thresholds of different wetland types in different regions.