In this paper, we investigate the dependence of gravitational Casimir effects on the frequencies of gravitational waves (GWs) in inspiraling neutron star (NS) binaries, with wide separation of . We introduce a mapping to describe the gravitational interactions and reflections on quantum scale and the frequency-dependent operator to depict the GWs/gravitons scattering. Accordingly, the gravitational fluctuation fields, i.e., GWs, can be decomposed as the gravitoelectric fields and gravitomagnetic fields, arising from the gravitoelectromagnetism due to the orbital motion of compact NS binaries, which can be unified as the gravitoelectric fields, because of their mutual induction. Because frequencies of GWs depend on both geometry and mass-density of the sources, we divide the calculations into geometric effects and mass effects. It is found that the dependence of gravitational Casimir energy arising from the quadruple moments on the GWs frequencies mainly give expressed to the post-Newtonian expansion coefficient. While the mass variation induced dependence on GW frequencies scales as in low-frequency GW sources, which reflects the temperature dependence of gravitational Casimir energy in wide inspiraling NS binaries.