Objective  Forest road network and its width is the basic demands of forestry production, transportation, and tourism. While giving maximum economic benefits, its function on forest fire patrol monitoring, emergency rescue, rapid transport of firefighters and equipment when happening fires also should be taken into account, as well as the function of block forest fire spreading and forest fire isolation.

  Method  The micro-mountains model of Pinus yunnanensis was constructed using fire dynamic simulation software PyroSim with parameters including slopes of 25°, 35° and 45°, wind speed of 1 , 2.5 and 4.5 m/s, and forest-road widths of 2, 4.5 and 6 m. And with the application of belt fire source with 12 m in length and 6 m in width, and heat release rate of 4.6 × 10⁴ kW/m², which simulated moderate-intensity forest-fire, we aimed to study fire-isolating functions at different forest-road widths.

  Result  The forest road width of 2 m failed to meet the need for fire protection and isolation. And the one with 4.5 m achieved relatively poor fire-isolating function performance. And the one with more than 35° slope and greater than 4.5 m/s wind speed was easy to lose its function. And 6 m width road got a strong fire isolation function. Comparing with the one that can better isolate medium-intensity forest-fire spreading condition can meet the one with less than 4.5 m/s wind speed and less than 45° slope. When wind speed reached more than 4.5 m/s, the fireproof blockade functions of forest-road width of 6 m may be lost. Generally, the central temperature of moderate-intensity forest fire was about 700−1 200 ℃. And corresponding heat release rate power can reach 3.0 × 10⁵ − 9.0 × 10⁵ kW. And it only took about 1 min to spread 10 m on the hill. And the burning rate of combustibles can reach above 40 kg/s in the 60 s.

  Conclusion  It is suggested to build the road with 6 m width in P. yunnanensis district in Yunnan Province of southwestern China, which can achieve better fire-prevention benefits. And road with width of 8−10 m is highly recommended in the forest area, where the stands with higher tree height all year round suffering high wind speed and slope greater than 45°. It also approve that the feasibility of simulating forest-road fire-isolating function by constructing the fire-site model with PyroSim, the results in this study have certain guiding significance on the rational designs of forest-road constructions, such as the determinations of maximum threshold values of fire prevention functions of forest-road with indexes of densities and widths, so can achieve certain economic benefits, as well as reductions of destructive powers of forest fires.