  The nonsingular bounce models usually suffer from the ghost or gradient
instabilities, as has been proved recently. In this paper, we propose a
covariant effective theory for stable nonsingular bounce, which has the
quadratic order of the second order derivative of the field $\phi$ but the
background set only by $P(\phi,X)$. With it, we explicitly construct a fully
stable nonsingular bounce model for the ekpyrotic scenario.
