Rock slope stability analysis can be applied for  transportation systems such as highways and railways. Failure of rock slopes includes a variety of rock falls, landslides and general  instability of rock slopes. This article is done in a rock slope which is composed of jointed tuff rocks. In the modeling of slope, the joints with different dips of 0, 30, 45, 60 and 90 degrees using phase2 software were analyzed. The most important factor that investigated in this study is the effect of pore pressure on the joints in such a way that the value of 0 Mpa to 0.5 Mpa has been considered .The results indicate that by increasing pore pressure on the joints, the critical SRF decreased and the highest decrease of SRF is occurred in the pore pressure of 0.1 Mpa.