Optomechanical dynamics in the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="script">PT</mml:mi></mml:math> - and broken- <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi mathvariant="script">PT</mml:mi></mml:math> -symmetric regimes

We theoretically study the dynamics of typical optomechanical systems, consisting a passive optical mode and an active mechanical mode, in $\mathcal{PT}$- broken-$\mathcal{PT}$-symmetric regimes. By fully analytical treatments for average displacement particle numbers, we reveal phase diagram under different conditions various regimes both $\mathcal{PT}$-symmetry stability system. find that by appropriately tuning either gain or coupling, transitions system can be flexibly controlled. As result, dynamical behaviors displacement, photons, phonons are radically changed Our shows $\mathcal{PT}$-symmetric devices serve as powerful tool manipulation motion, phonons.