In order to study the thixotropic properties of casting aldol based polymer bonded explosive, the effect of RDX gradation and content of RDX particles on the thixotropic properties of the slurry was explored by a thixotropic loop method. The area of hysteresis loop was used to characterize the thixotropic extent. Results show that the slurry system is a pseudoplastic fluid. The slurry with different RDX gradation has different degree of thixotropy. The higher the number of RDX gradation or the larger the RDX particles, the smaller the thixotropy of slurry. The higher the content of small particles, the greater the influence of gradation of large and middle particles on the decreasing extent of thixotropy of slurry. Thixotropic extent of the slurry reveals a positive correlation with the content of small RDX particles, and a negative correlation with the content of large RDX particles.