The loss of N in farmland is an important cause of agricultural non-point source pollution, which seriously impacts the aquatic environment.  A two-year (2017–2018) experiment was conducted to investigate the characteristics of runoff and N losses under different tillage practices.  Taking downslope ridge planting and cross ridge planting as the experimental treatments, the characteristics of surface runoff, interflow, and N losses in sloping farmlands with yellow soil were studied throughout the maize growth period.  As the rainfall increased, the surface runoff and interflow also increased.  The surface runoff and N losses in the surface runoff of downslope ridge planting were significantly higher than those of cross ridge planting.  The interflow volumes and N losses in the 0–20 and 20–40 cm soil layers of the cross ridge planting were significantly higher than those of the downslope ridge planting.  The total N (TN) losses from surface runoff accounted for 54.95–81.25% of the N losses from all pathways.  Therefore, we inferred that surface runoff is the main pathway of N losses.  Dissolved total N (DTN) was the main form of N loss under different tillage measures, as it accounted for 55.82–94.41% of the TN losses, and dissolved organic N accounted for 52.81–87.06% of the DTN losses.  Thus, we inferred that dissolved N is the main form of N loss.  Future research must focus on the prevention and control of the N losses during the maize seedling stage to reduce the environmental pollution caused by ammonium N through runoff.