Abstract: Study on different mechanical properties of structural joints in loess and their regional,systematical features made us to suggest that two sets of their torsion-fracture planes are representative of orientations of maximum shear stress of neotectonic stress field.The loess structural joints systems and controlled by them gully and ravine network on soil layer can be used in reconstruction of relevant Q2-3tectonic stress field.It indicates that the structural joints are the main channels and locus for the groundwater migration in loess region and the structural basis for geologic hazards,such as ground fissuring,landslide,collapse,and water loss in the loess region.The structural joints are the weak surfaces in loess strata,and at them the weathering process and stress erosion start.and hence the erosional landforms,such as ground pan,cave.hole,ridge,pillar,wall.gully,can be gradually formed.Study on structural joints in loess has its practical significance in reconstruction of neotectonic stress field,in prediction of ground fissure and seismic activity, in control on water loss and landslide hazard, in engineering evaluation of regional stability,in understanding regularities of erosional landforms,as well as in searching ground water in arid and semiarid loess regions.