This study focuses on enhancing the toughness and strength of negative Poisson's ratio metamaterial (NRPM) through pyrolysis and carbonization of a polyethylene glycol diacrylate photocurable resin and in-situ self-assembling into polymer-graphene, and the mechanical properties of NRPM were significantly improved by the synergism of polymer-graphene and the resin matrix. Experimental results illustrated that maximum load of completely carbonized NRPM was 144.4 N, which was almost nine times higher than that of the untreated prototype. Moreover, the elastic modulus of completely carbonized NRPM was 2.46 MPa, which was only 1/8 of the untreated prototype, indicating a significant improvement in flexibility. Molecular dynamics simulations were conducted to study the self-assembly mechanism of polymer-graphene, conjunction with experiments, which offers new insights into the evolution of photocurable resins into polymer-graphene and opens up possibilities for fine-tuning the proportion of polymer-graphene and nanostructures for a broad range of multi-scenario applications of NRPM.