  We investigate the linear cosmological perturbations of Ho\v{r}ava-Lifshitz
gravity in a FRW universe without any matter. Our results show that a new gauge
invariant dynamical scalar mode emerges, due to the gauge transformation under
the "foliation-preserving" diffeomorphism and "projectability condition", and
it can produce a scale invariant power spectrum. In the infrared regime with
$\lambda=1$, the dynamical scalar degree of freedom turns to be a non-dynamical
one at the linear order level.
