In order to investigate the effects of binder component on the creep properties of polymer-bonded explosive (PBX), three-point bending creep behaviors of 1,3,5-triamino-2,4,6-trinitrobenzene (TATB)-based PBX and its styrene copolymer modified formulation were studied by dynamic mechanical analyzer. The experimental results showed that owing to the addition of reinforcing agent (styrene copolymer) with high glass transition temperature and high mechanical strength, the creep resistance performance of the modified formulation was improved with reduced creep strain and constant creep rate and prolonged creep failure time. A six-element mechanical model was applied to simulate the creep behaviors of TATB-based PBX and its modified formulation. The constitutive equation of creep curves under different conditions were obtained by nonlinear fit. The predicted theoretical results coincided quite well with the experimental data.