Using molecular dynamics (MD) simulations, we have measured the indirect interacting force between surface-separated nanoparticles (NPs) within athermal polymers. Our simulations confirm the existence of repulsion between NPs with separation beyond the range of attractive forces. We demonstrate that both attractive and repulsive forces are monotonically strengthened by increasing polymer concentration and/or enlarging the size of NPs. The indirect interacting force as function of separation between NPs has no dependence on polymer chain length for semi-dilute polymers. Moreover, we have calculated the radial distribution functions of monomers surrounding NPs, the density profiles appear to corroborate the measured forces. (C) 2015 Published by Elsevier B.V.