To explore the effect of HMX gradation on the rheological properties of the aldol based polymer bonded explosive, the material state under different HMX particle gradation ratio was investigated by power law model and Casson model. The results show that the material is a pseudoplastic fluid with thixotropy. The non-Newtonian index (n value) is negatively correlated with the content of small particles. The viscosity of the material has the maximum value at low shear rate of 2.15 s^-1 and positive linear relationship at high shear rate of 53.85 s^-1 with the small particles content. The yield value of the material is negatively correlated with the content of small particles. Moreover, the content of the middle particles has the greatest effect on the yield value. Considering that the material with higher n value, lower viscosity and lower yield value has the better rheological properties.