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We propose a scheme to cool a mechanical resonator to its ground state in a P T -symmetric cavity optomechanical system. The system features a loss optomechanical cavity coupled to a gain cavity, with the loss cavity being driven by an amplitude-modulated laser field. Utilizing numerical simulation methods, we study the stability of the system and the cooling properties of the mechanical resonator in detail. We find that the system is almost stable within the unbroken P T -symmetry region. The mechanical resonator achieves ground state cooling in both resolved-sideband and unresolved-sideband regimes. Notably, the cooling efficiency is significantly higher in the unbroken P T -symmetry region compared to its broken counterpart. P T -symmetry plays a pivotal role in optimizing the cooling performance of the mechanical resonator. These findings open new avenues for quantum manipulation using P T -symmetric systems, with potential applications in macroscopic optical devices. • P T -symmetric cavities with modulated drives stabilize in unbroken phase. • Mechanical cooling achieves in both resolved and unresolved-sideband regimes. • Cooling efficiency is significantly higher in the unbroken P T -symmetry region. • Cooling in the gain-loss system exhibits enhanced robustness against thermal noise.