Abstract: The intensified impact of climate change and anthropogenic activities has changed the stationary characteristics of the hydrological extreme series, thus posing a challenge on the Traditional Hydrological Frequency Analysis (THFA) method. Therefore, a new theory and approach is required for analyzing non-stationary hydrological frequency. In this paper, further discussions are conducted about the fundamental idea of Equivalent Reliability (ER) approach, and ER application for the design flood estimation under a changing environment has been expanded. The ER approach is expected to address two key issues: ① to estimate the design flood with a given design standard for a project yet to be constructed; ② to adjust the design flood for an already constructed project for its adaptation to the changing conditions. The 59 years of 15-day flood volume series from 1956 to 2014 is used to demonstrate the ER approach, and analysis is conducted for the impact of parameter uncertainty on design flood. The results show that the design flood with a given return period under non-stationary conditions varies with the engineering design lifetime, and the uncertainty of the design flood estimation increases when the engineering design lifetime extends.