In recent years, with the influence of environmental changes such as climate and substratum conditions, the dramatic reduction of the Yellow River"s water flow has become one of the serious problems facing society today. And the Loess Plateau, as the main runoff area in the Yellow River basin, has practical significance in exploring the changes of its runoff characteristics and runoff patterns. This study analyzes the changes of annual rainfall runoff, field floods, and land use features, as well as the relationship between rainfall and runoff, based on precipitation and flood data in Nanxiaohegou watershed, using statistical methods. It also identifies the trend of runoff pattern changes in the Nanxiaohegou watershed from 1981 to 2020 using hydrological methods and principles. The results show that: (1) The annual rainfall runoff, rainfall-runoff characteristics, and land use patterns in the Nanxiaohegou watershed are the important factors that lead to the change of runoff patterns in the watershed. (2) Among the 46 typical sub-flood events in the watershed, the overall runoff mode is mainly over-infiltration and mixed runoff, accounting for 80.4% of the total flood events. The proportion of superficial runoff decreased by 57.5%, while the proportion of mixed runoff increased by 87.1%. The proportion of full runoff changed little. (3) From the comprehensive indicators that affect the runoff pattern in the watershed, the reference period is dominated by mixed runoff mode with superficial runoff as the main runoff mode, while the change period is dominated by mixed runoff mode. The research results can provide scientific references for the study of runoff patterns and ecological governance in the Loess Plateau region.