  For there is always a wrong sign in the mass of graviton in the so-called
perturbation expansion approximation of both Minkowski and de Sitter
spacetimes, the existence of gravitational wave from the metric perturbation of
de Sitter spacetime is doubtful. We try another way to start from the
assumption that the gravitational wave equation should be both general
covariant and conformal invariant and find that graviton is no longer a part of
metric field, it has an effective mass of $m_g=\sqrt{R/6}=% \sqrt{2\Lambda/3}$
with correct sign in de Sitter spacetime, though it's intrinsic mass remains
zero.
