This research selects several main flow stations in Korea. The validity of application of the observed flow is assessed the floods. In order to estimate design floods by using the observed and the higher probability weighted moment (LH-moment). This research estimates the design floods not by using all annual maximum flood flows from the past initial observation point to the present point, but by using annual maximum flood flows from the initial observation point to early 1990s and subsequent year each by each after the last year used in the analysis. This research will gives the knowledge of the determination of the right time to change design floods due to the weather abnormalities caused usually by the global warming, and provides stable conditions for designing hydraulic structures suited to Korean conditions. The research results are expected to be certainly applied in establishing Korea's disaster prevention measures, as well as in constructing a management system for the hydraulic structures in the related Ministries and local governments.