Intragranular defects inside RDX/HMX were studied by optical microscopy with matching refractive (OMS), sink-float method (SFM), and micro-focus CT (μCT) techniques. OMS results revealed the phenomenon that RDX/HMX had more defects and cracks than RS-RDX/RS-HMX. μCT results indicated that RDX/HMX had more defects with larger volume than RS-RDX/RS-HMX. The gap test showed that critical shock pressure/gap thickness was 6.4 GPa/19.4 mm for PBX based on RDX, while they were 7.5 GPa/17.5 mm and 8.6 GPa/16.2 mm for PBX based on M-RDX and RS-RDX, respectively. Meanwhile, an analysis of the relationship between defects inside RDX/HMX crystal and shock sensitivity was made. Finally, the shock pressure response under impact loading was investigated by discrete element method.