The dynamics of spin polarons (spin bags) in the quasi-one-dimensional spin-density-wave background is numerically studied using the extended Peierls-Hubbard model. Interchain couplings are incorporated to the model as a staggered magnetic field. Time-dependent unrestricted Hartree-Fock equations and Newtonian equations are solved using Suzuki’s decomposition of exponential operators. In the Hubbard model, the spin polarons with antiparallel spin polarizations attract each other. When the nearest-neighbor Coulomb repulsion is included, the interaction changes to a repulsive type. Further addition of an intersite electron-phonon coupling leads to an attractive interaction.