The continuous leakage spilling fire is one of most serious patterns of liquid fire owing to the continuous expansion of burning area. This work aims to study the characteristics of velocity and burning rate of large-scale spilling fire. Based on 6 m x 0.8 m stainless steel spilling trench, the trajectory and instantaneous velocity of spilling fire of n-butanol fuel in steady flow are measured. The non-slope spilling fire is separated into three stages: slowly increasing, oscillatory acceleration and rapidly ascending while there are only slowly increasing and rapidly ascending stages for slope-aided spilling fires. The critical velocity of liquid-and gas-phase spilling fire with a slope is significantly larger than that without slope, whereas the induction time of transformation of liquid-and gas-phase stage is shorter. The liquid evaporation model is developed to calculate the critical evaporation rate for liquid-and gas-phase stage, which is very close to experimental value. The curve of real-time mass burning rate shows a monotonous increase tendency with fire advancement time which is fully consistent with the theoretical analysis of two-dimensional heat transfer. The current research has a guiding significance for prediction of spilling fire spread under continuous leakage.