Some researchers have been carried out on analysis of the influence of the full grouted prestressed anchor shape of borehole wall on its carrying capacity. Based on the self-affine fractal feature of anchor borehole wall structural plane, the relation equation among structural plane shear strength, liquid injection pressure, tensile load and structural plane fractal dimension D was built, the instability judgment criterion of anchoring bearing strata and rock structural plane was determined, the solving equations of disintegrated rock support density were derived. Based on the experimental results, the theoretical basis of support design under the disintegrated rock condition was offered.