HTPB/CL-20 castable booster explosives were prepared successfully by a cast-cured process. Scanning electron microscope (SEM) and the charge density test were employed to characterize the molding effect of HTPB/CL-20 explosives. The propagation reliability, detonation velocity, mechanical sensitivity, thermal decomposition characteristics and thermal stability of the HTPB/CL-20 explosives were also measured and analyzed. The results show that, when CL-20 content is less than 91 wt.-%, the charges with better molding effect were obtained easily. The critical diameter of HTPB/CL-20 explosives is less than 1 mm, which exhibits good propagation reliability. When the density of HTPB/CL-20 charge with 91 wt.-% CL-20 is 1.73 g cm(-3), its detonation velocity can reach 8273 m s(-1). Moreover, this kind of explosives has low mechanical sensitivity and good thermal stability.