Abstract: In view of the complicated operation of the current crack detection method of hydraulic support, a weak magnetic nondestructive detection method for cracks in the top beam of hydraulic support based on geomagnetic field excitation is proposed. Firstly, the stress field of the crack in the top beam of hydraulic support is analyzed by using COMSOL Multiphysics simulation software. Secondly, based on the principle of weak magnetic nondestructive testing, the geomagnetic field is loaded in the simulation space. The superimposed field formed by the magnetized material with crack defects and the geomagnetic field is obtained and analyzed. The results show the following points. ① There is stress concentration phenomenon in the top beam defect of hydraulic support. The lower the stress is, the greater the stress is. The crack expands from the outside to the inside to both sides. The failure risk of the top beam can be effectively reduced by finding the surface crack in time. ② When the length and depth of the crack defect are fixed, the horizontal distance between the valley and the peak and the peak value of the magnetic flux density mode curve of different width cracks increase with the increase of the width. The valley value decreases first and then increases with the increase of the width. The amplitude of the flux density mode increases with the crack width. The variation rate of the difference between the adjacent maximum valley and peak of the flux density mode decreases with the crack width. The change amplitude of magnetic flux density is positively correlated with the change of crack width. ③ When the length and width of the crack defect are fixed, the valley value of the magnetic flux density mode curve of different depth cracks has little difference. The left peak value increases with the increase of the width. The right peak value decreases with the increase of the width. With the increase of the crack depth, the change amplitude of the flux density mode increases. The change rate of the difference between the adjacent maximum valley and peak of the flux density mode is almost constant. The change amplitude of magnetic flux density is positively correlated with the change of crack depth. The magnetic flux density is more sensitive to the change of crack width than to the change of crack depth. ④ When the length, width and depth of the crack defect are fixed, the change in the direction of the crack does not affect the judgment of crack defects.