  Gravitational wave (GW) data can be used to test the parity symmetry of
gravity by investigating the difference between left-hand and right-hand
circular polarization modes. In this article, we develop a method to decompose
the circular polarizations of GWs produced during the inspiralling stage of
compact binaries, with the help of stationary phase approximation. The foremost
advantage is that this method is simple, clean, independent of GW waveform, and
is applicable to the existing detector network. Applying it to the mock data,
we test the parity symmetry of gravity by constraining the velocity
birefringence of GWs. If a nearly edge-on binary neutron-stars with observed
electromagnetic counterparts at 40 Mpc is detected by the second-generation
detector network, one could derive the model-independent test on the parity
symmetry in gravity: the lower limit of the energy scale of parity violation
can be constrained within $\mathcal{O}(10^4{\rm eV})$.
