A self-developed laboratory-sized spilling trench is used to study the characteristics of continuously spilling fire spread over n-butanol fuel under different slope angles (0 degrees, 1 degrees, 2 degrees, 3 degrees, 4 degrees) and discharge rates (0-500 mL/min). The hydrodynamic analysis is conducted to account for the variation of flow parameters of unburned liquid based on the theory of open-channel gradual flow. The spill flow velocity increases whereas the thickness of fuel layer decreases along the inclined spilling trench. The flame height versus discharge rate is divided into three regimes, namely the increasing regime at Q < 165 mL/min, the decreasing regime at 165 <= Q 370 mL/min, and the stable regime at Q >= 370 mL/min, where Q is the discharge rate. The effect of discharge rate on flame height is related to the heat transfer of fuel surface. With an increase in discharge rate or slope angle, the oscillatory pattern of spilling fire changes from "jumping-retreating-crawling" to "jumping-crawling" and eventually to "uniform". The velocity of spilling fire is strongly enhanced by the slope angle and the discharge rate because the fuel vapor is driven by dragging effect of no-slip boundary condition on the liquid surface.