Abstract: Under influence of climate change and human activities, the watershed water cycle and its associated processes have changed, resulting in the inconsistency characteristics of hydrological processes, so the original calculation methods of design flood cannot meet the needs of design of water conservancy project and flood control under new environment. In view of this, taking Liaoning Province as an example,we study on the calculation methods of design flood under variable environment. 10 kinds of frequency distribution curves, such as Pearson III and EBⅫ, have been used for flood frequency analysis, and the EBⅫ pattern has been established for flood frequency analysis in arid and semi-arid areas. The fitting degrees of 22 stations in the western Liaoning Province are all above 0.95. Based on GAMLSS model, a non-uniform calculation model of design flood in Liaoning Province has been established for the purpose of reflecting the influence of variable environment on design flood. In order to improve accuracy, the calculation method of design flood in un-gauged basins in Liaoning Province has been improved based on the data in recent 20 years. The results have been applied in the design of water conservancy project in Liaoning Province, and have been popularized in Songhua River and Liaohe River Basin. It is also of reference value to the calculation of storm flood in other areas.