The propagation of forest fires is primarily characterized by surface fires. A substantial body of research has been devoted to investigating surface fires, with particular attention paid to the interactive effects of low slope angles and wind on their propagation characteristics. In contrast, studies on the coupled effects of fuel load and slope on surface fire spread characteristics remain relatively limited. In this study, a slope‑adjustable experimental setup was used to conduct comparative experiments on surface fire spread under varying slope angles (0°, 20°, 30°, 40°), fuel loads (0.8, 1.0, 1.2 kg/m²), and fuel types (Pinus koraiensis and Quercus mongolica). Quantitative analyses were performed on the evolution of fire front shape, flame geometry parameters, rate of fire spread, and flame plume temperature. The results revealed that the time required for the fireline pinch‑shaped front to transition from its initial state to a steady state during surface fire spread on a variable slope exhibited a negative correlation with slope angle. When the slope angle was below 30°, its influence on the flame inclination angle was relatively weak; however, when the slope angle exceeded 30°, this influence became even less pronounced. Additionally, fuel type notably affected both the spread rate and flame length. Under identical operating conditions, the flame length and spread rate of Pinus koraiensis were greater than those of Quercus mongolica. The spread rate increased significantly when the slope angle exceeded 30°. Furthermore, correlation analysis was used to evaluate the effects of slope angle and fuel load on the characteristic parameters of fire spread. The results showed that slope angle significantly influenced flame angle, flame length, spread rate, and combustion temperature, whereas fuel load mainly determined flame length, spread rate, and combustion temperature.