  Corresponding to the similarity between the Lorentz gauge $\partial_\mu
A^\mu=0$ in electrodynamics and $g^{\mu\nu}\Gamma^\rho_{\mu\nu}=0$ in gravity,
we show that the counterpart of the radiation gauge $\partial_iA^i=0$ is
$g^{ij}\Gamma^\rho_{ij}=0$, in stead of other forms as discussed before.
Particularly: 1) at least for a weak field, $g^{ij}\Gamma^\rho_{ij}=0$ fixes
the gauge completely and picks out exactly the two physical components of the
gravitational field; 2) like $A^0$, the non-dynamical components $h_{0\mu}$ are
solved instantaneously; 3) gravitational radiation is generated by the
"transverse" part of the energy-momentum tensor, similar to the transverse
current $\vec J_\perp$. This true" radiation gauge $g^{ij}\Gamma^\rho_{ij}=0$
is especially pertinent for studying gravitational energy, such as the energy
flow in gravitational radiation. It agrees with the transverse-traceless (TT)
gauge for a pure wave, and reveals remarkably how the TT gauge can be adapted
in the presence of source.
