The effect of the cascade hydroelectric development on the flood process and characteristics in the Datonghe River Basin was qualitatively and quantitatively analyzed by using the observed flood data and water resources survey data. The mathematical model was established to analyze the relationship between the number of hydropower stations, flood fluctuation rate, and flood fluctuation frequency at the representative hydrometry stations. The results show that the flood process changes frequently, flood fluctuation rate and fluctuation frequency increase along with the number of the hydropower stations increasing. The cascade hydroelectric development makes the maximum flood peak flow increase by 19.7%-21.5%, the flood routing duration decrease by 6.1%, while less effect on the total amount of a flood. The research on the influence regularity of human activities on hydrological process is very significant for strengthening unified dispatching of hydropower stations in a river basin, water sustainable utilization of water resources and water ecological civilization construction.