The research of road net system in the theoretic field in our country used to stay at the quota of road density and was never transferred to the controlled quota for a proper span between forest roads and proper arrangement of forest roads, In order to open up a new way for intensive management of wood production, based on massive investigations and practical survey, this paper creates the theoretic equation identifying the best and the limitation of spans between forest roads, and indicates the pattern and the method arranging road nets in harvest areas as well as uses the best span between forest roads as a controlled quota of forest roads in harvest areas in the light of the principle of the low est total cost in skidding and transportation.