Abstract: The extensive development of vertical joints is one of the major features in the loess region. The joint destroys the integrity of the loess slope, reduces the slope stability. First of all, through the field investigation and analysis of the characteristics of loess joint development, it was found that joint strike crosses obliquely slope inclination and is controlled by the latter. Secondly, according to the analysis of different regional stress of slope, soil of tableland area is mainly impacted by saturated yielding tension, and soil in the slope zone is mainly effected by thrust produced by horizontal unloading, joint development in slope area is divided into saturated yielding joint development area, tension joint development area, compression joint development area and the joint development area of unloading caused by excavation. Finally, calculation of stability was carried out for slopes with or without joints. The calculation results are in accordance with the theoretical analysis.