Under complex loads, theoretical methods are used to solve the mechanical properties of subsurface deflection cracks in a semi-infinite plane. The problem included two parts according to the method we followed, the superposition theorem. One used elastic mechanics; the other used the principle of distributed dislocation. And Gauess-Chebyshev numerical solution method was used to solve. The two were jointly used to solve the mechanical parameters. SIF graphs of the crack tip at all kinds of load ratios of the deflection, depths and length ratios cracks at the corresponding deflection angles were obtained, and the crack propagation direction under this working condition was analyzed. SIF increased with the increase of the length of the deflection part, SIF decreased as the depth of the crack buried increased; and when the ratio of transverse crack and shearing load grew, the SIF also increased. When the crack was closer to the surface, it was easier to expand and grow with the increase of the deflection angle in the clockwise direction. When the load ratio, crack embedding depth, and length are relatively large, the cracks are more likely to propagate to the surface to form open cracks, the cracks are propagated in a clockwise direction and varies with the deflection angle.