In arid and semi-arid regions of China, strong human disturbance causes significant changes in urban river flood process, which affects flood control and water resource planning results. In this paper, we study the effects of land use change and reservoir construction and operation on the changes of rainstorm flood processes in different recurrence periods by the Modified Cell Distributed Rainfall Run-off Model (MCDRM). We construct the rainstorm flood model and verify the model parameters and simulation results according to the calculation results of traditional rational formula, take the urban Bahe River at the northern foot of Qinling mountains as an example. The results showed that the trend of increase of urban land area and water area in the basin increased, and the intensity of water resources development and utilization increases obviously, due to the urbanization of xi 'an city speeds up after 2000, and then the construction of the “eight rivers moisten Chang 'an” project. High intensity human activities change underlying surface conditions in runoff generation and confluence of the flood in Bahe River Basin; the designed flood peak volume and total flood amount decreased since 1980. Compared with 1985, the designed flood peak flow with a recurrence period of 10 years, 20 years, 50 years and 100 years in 2015 decreased by 22.98% on average, and the total designed flood runoff decreased by 21.4% on average. Among them, the design flood peak volume decreased by a maximum of 23.88% at 100-year recurrence period, and the total amount of standard design flood runoff decreased by 21.51% at 20-year recurrence period. This paper carried out the study on the simulation and response change of rainstorm flood caused by human activities in urban rivers, which is based on the improved grid distributed rainfall-runoff model, and the results can provide a new reference for the design flood review and calculation of small and medium-sized watersheds in arid and semi-arid areas.