  We introduce a novel concept of the {\em pseudo} parity-time ($\mathcal{PT}$)
symmetry in periodically modulated optical systems with balanced gain and loss.
We demonstrate that whether the original system is $\mathcal{PT}$-symmetric or
not, we can manipulate the property of the $\mathcal{PT}$ symmetry by applying
a periodic modulation in such a way that the effective system derived by the
high-frequency Floquet method is $\mathcal{PT}$ symmetric. If the original
system is non-$\mathcal{PT}$ symmetric, the $\mathcal{PT}$ symmetry in the
effective system will lead to quasi-stationary propagation that can be
associated with the \emph{pseudo $\mathcal{PT}$ symmetry}. Our results provide
a promising approach for manipulating the $\mathcal{PT}$ symmetry of realistic
systems.
