In order to investigate the effect of the position and angle of the pre-existing cracks on the shear capacity of beams without web reinforcement, a number of experiment beams with pre-existing cracks were fabricated, the three-point bending experiment of the beam was carried out. The influence of pre-existing cracks located in the basic arch of the beam span and the beam side on the shear capacity of beams without web reinforcement and the law of crack propagation were studied. The results showed that the pre-existing cracks on the beam had a weakening effect on the shear capacity of the beam, which made the beam more prone to diagonal tensile failure. Under the same conditions, when the crack tip of the pre-existing crack in the beam span was closer to the middle point of the bottom of the beam, the greater the weakening effect on the shear bearing capacity of the beam without web reinforcement. When the coincidence degree of the angle of the pre-existing cracks on the beam side and the basic arch was higher, the greater the weakening effect on the shear bearing capacity of the beam without web reinforcement, and the cracks at the bottom of the beam propagate through the two crack tips of the pre-existing cracks was easier. Conversely, the cracks at the bottom of the beam could extend to the middle of the pre-existing cracks.