Abstract: To investigate the effects of shear stress to failure wave, series of experiments including oblique planar impact with inclination angle 10 and 15 degree, impact loading velocity ranging from 150 m/s to 400 m/s for K9 glass of central cut sample, are carried out in the present paper. Experimental results show that there existed a wave front with wave velocity exceeding that of longitudinal wave between the loading transversal wave and the unloading longitudinal wave. The wave has affected the amplitude of the unloading waves. Since the wave might be generated for the existing of central surface in central cut sample, some experiments including oblique planar impact with inclination angle 10 degree and impact loading velocity ranging from 70 m/s to 300 m/s for K9 glass of across cut sample are carried out in succession to eliminate the effect of central surface. In these experiments, the wave velocity of failure wave is determined to be 0.98-1.4 km/s and corresponding critical value for failure wave under combined pressure and shear impact loading are pressure 0.86-101 GPa and shear 0.053-0.071 GPa. All these show that shear stress may greatly decrease the critical value for failure wave. Some preliminarily discussions on dynamic friction coefficients and sliding velocity of impact surface are also conducted.