In order to explore the influence of the liquid column pressure on the stability of borehole， study the stress characteristics and crack propagation mode of the surrounding rock under the action of the liquid column pressure in the borehole and the ground stress， the triaxial confining pressure hydraulic test method is adopted to carry out the laboratory test on the packsand by changing the confining pressure and the water pressure in the borehole， and the inner observation of the packsand is carried out by CT scanning method. The results show that：（1）when the confining pressure is constant， the variation trend of deviatorial-strain curve of packsand at each stage is greatly affected by bore water pressure， and the peak strength， residual strength and axial peak strain are positively correlated with confining pressure and bore water pressure. The action of water pressure in the pore delays the process of mechanical failure in the compressive yield stage of packsand and increases the degree of ductile fracture of packsand.（2）CT scan shows that under certain confining pressure， the angle between the principal shear fracture plane and the axial direction of the packsand decreases with the increase of the water pressure in the pore， and the shear crack track gradually deflects from the outside of the rock sample to the central pore wall. With the increase of water pressure in the hole， the collapse mode of rock block in the hole wall changes from centralized collapse to scattered collapse. The larger the water pressure in the hole， the smaller the collapse area and collapse degree of the rock in the hole wall.（3）Increasing water pressure can improve the stability of borehole and reduce the possibility of borehole instability.