Abstract: Loess joints can be generally classified into primary joints,structural joints,weathering joints and unloading joints.Primary joints and structural joints are widespread in northern Shaanxi.Primary joints are widely distributed in Malan loess and are characterized by large density and long stretching.Structural joints,with distinct directivity and spatial difference from region to region,are distributed in Lishi loess.Stability of a highway slope varies with the orientations of loess joints.When the joints have their orientations similar to that of the slope,they can have the maximum effect to reduce slope stability.The vertical joints have less efect.When joints are perpendicular or intersect the slope,their effects are minor..Several sets of joints can form some regular discontinuity patterns on slope surfaces.In the three dimensional space,they can form the tabular,sphenoid,and columnar structure patterns.The structural bodies with different forms have different effects on the stability of slopes.The authors also discuss the method of calculating the stability of slopes with oblique joints.