Intragranular defects inside RDX/HMX were studied by optical microscopy with matching refractive (OMS), sink-float method (SFM), and micro-focus CT (CT) techniques. OMS results revealed the phenomenon that RDX/HMX had more defects and cracks than RS-RDX/RS-HMX. CT 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 6.4GPa/19.4mm for PBX based on RDX, while they were 7.5GPa/17.5mm and 8.6GPa/16.2mm 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.