Irrigation projects have diverted water from the lower reaches of the Yellow River in China for more than 50 years and are unique in the world. This study investigated the effect of irrigation practices on the transfer and regional migration mechanisms of nitrate (NO3(-)) in surface water and groundwater in a Yellow River alluvial fan. Hydrochemical indices (EC, pH, Na(+), K(+), Mg(2+), Ca(2+), Cl(-), SO4(2-), and HCO(3-)) and stable isotopic composition (δ18O and δD) were determined for samples. Correlation analysis and principal component analysis (PCA) were performed to identify the sources of water constituents. Kriging was employed to simulate the spatial diffusion of NO3(-) and stable isotopes. Our results demonstrated that the groundwater exhibited more complex saline conditions than the surface water, likely resulting from alkaline conditions and lixiviation.