Abstract: The reasonable drilling fluid densities are vitally important for the stability of borehole surrounding rock. Its continuous process of borehole shearing damage is simulated based on the principle of Drucker-Prager and through the way of finite element analysis, and the correlation between the damaging scale and the density of drilling fluid is also presented. The simulating tendency is basically concordant with the field condition and the laboratory testing result, and this study provides a quantitative backup for analyzing the influence of drilling fluid density on the damaging area of borehole surrounding rock.