Thermoplastic vulcanizates (TPVs) based on high impact polystyrene (HIPS)/styrene-butadiene-styrene block copolymer (SBS)/styrene-butadiene rubber (SBR) blends were prepared by dynamic vulcanization, with the TPVs being reinforced by carbon black (CB). Experimental results indicated that mechanical properties of dynamically vulcanized HIPS/SBS/SBR blends were enhanced remarkably by the incorporation of CB. The fracture surface morphology of the reinforced HIPS/SBS/SBR/CB TPVs was relatively flat. The Mullins effect could be observed in the stress-strain curves of HIPS/SBS/SBR TPVs and HIPS/SBS/SBR/CB TPVs during the uniaxial loading-unloading cycles. Compared with HIPS/SBS/SBR TPVs, CB-reinforced HIPS/SBS/SBR TPVs had the relatively higher stress, residual strain and internal friction loss.