To study the effect of initial damages on the structural change and damage behavior of polymer bonded explosive (PBX) under external force, the initial damages was simulated by the way of prefabricated defects, three groups of simulated material samples of PBX, including the sample without prefabricated defect, sample with oblique 45° non-through defect and sample with oblique 45° through defect were prepared, in-situ studies were performed on X-ray CT system. using the loading way of improved arc compress head Brazilian test. Information on three dimensional morphology, size and spatial distribution of cracks and pores were obtained by digital image processing techniques.The finite element simulation of the test was carried out by using ABAQUS software. Results show that when the prefabricated defect has a certain angle to the loading direction of Brazilian test, the prefabricated defect makes the symmetry of its loadig way destroy and the damage behavior of the sample will also change accordingly. The influence of non-through defects and through defects on the damage behavior of samples is very different, the non-through defect may result in stratification phenomenon of the sample. namely the effect of surface defects on the damage behavior of the samples is mainly concentrated in the defective part. The simulation results are in good agreement with the experimental, and explaine the experimental phenomena to some extent.