Abstract: Aiming at the influence of transition Between meteorological drought and flood on runoff ,Based on the daily precipitation and flow data in Jialing River Basin ,the spatio- temporal distribution and evolution laws of drought - flood abrupt alternation were analyzed by long - term and short - term drought - flood abrupt alternation indexes ,and the response degree of runoff changes to different types of abrupt alternation was quantitatively evaluated. The results showed that there have been 8 drought - flood abrupt alternation events in the Jialing River Basin during the flood season from 1977 to2022 ,6 of which occurred in the 2000s and after. Spatially ,the frequencies of drought - flood abrupt alternation in southern areas ,central areas ,and the surrounding areas of the northwest were the largest above 17% . On the monthly scale ,the highest frequency appeared in the period from June to July ,which was beyond 20% . When flood - to-drought turns occurred in the flood season ,the runoff of BeiBei ,Luoduxi ,Wusheng , and Xiaoheba stations in the first half flood season increased by 57 . 52% ,38 . 74% ,85 . 50% ,and 99 . 73% on average , and reduced by 20 . 82% ,49 . 83% ,22 . 64% and 14 . 53% on average in the second half period. Inversely , under the influence of the drought - to- flood events ,the first half runoff of those stations decreased by 31 . 17% ,45 . 77% ,28 . 83% ,and 26 . 16% on average ,and increased by 31 . 45% ,47 . 17% ,24 . 31% , and 3 . 27% respectively in the latter half period. The monthly scale also showed similar laws ,indicating that drought - flood abrupt alternation had a significant impact on the runoff of the Jialing River. The research results can provide scientificreference for the operation of cascade reservoirs and watershed water security .