  Resonant scattering (RS) of X-ray line emission in supernova remnants (SNRs)
may modify the observed line profiles and fluxes and has potential impact on
estimating the physical properties of the hot gas and hence on understanding
the SNR physics, but has not been theoretically modeled ever. Here we present
our Monte-Carlo simulation of RS effect on X-ray resonant-line emission,
typified by O VII He$\alpha$ r line, from SNRs. We employ the physical
conditions characterized by the Sedov-Taylor solution and some basic parameters
similar to those in Cygnus Loop. We show that the impact of RS effect is most
significant near the edge of the remnant. The line profiles are predicted to be
asymmetric because of different temperatures and photon production efficiencies
of the expanding gas at different radii. We also predict the surface brightness
of the line emission would decrease in the outer projected region but is
slightly enhanced in the inner. The G-ratio of the OVII He$\alpha$ triplet can
be effectively elevated by RS in the outer region. We show that RS effect of
the O VII He$\alpha$ r line in the southwestern boundary region of Cygnus Loop
is non-negligible. The observed OVII G-ratio $\sim$1.8 of the region could be
achieved with RS taken into account for properly elevated O abundance from the
previous estimates. Additional simulation performed for the SNRs in
ejecta-dominated phase like Cas A shows that RS in the shocked ejecta may have
some apparently effects on the observational properties of oxygen resonant
lines.
