Soil erosion is of the most important environmental challenges and factors of forest damage, which is, occur because of the land use change, road construction and lack of vegetation cover. Forest soil is naturally penetrable but forest roads are not. This issue causes the flows runoff on road surface and washes soil particles. Thus, forest roads must be planned and constructed accurately. So, this study attempts to use the ability of GIS and AHP to plan optimal forest road with considering effective factors on land stability including slope length and steepness (LS factor), soil erodibility (K factor), hydrographic networks, geology, vegetation cover, aspects and elevation maps. After providing each of thematic layer and determining their priority by Analytical Hierarchy Process, the overlay process was conducted and stability map was prepared in four classes. The road network was planned using by PEGGER (an extension of ArcView 3.0 software) on stability map. The planned variants and existence road network was compared using Chi-square test. Results showed that the planned road network is better than existence road network at probability level of 95%, because it passed more from stable and suitable area. The results of this research can be effective to optimize the design of forest road network and can reduce the environmental damage.