  Quantum localization in 1D non-Hermitian systems, especially the search for
exact single-particle mobility edges, has attracted considerable interest
recently. While much progress has been made, the available methods to determine
the ME of such models are still limited. In this work, we propose a new method
to determine the exact mobility edge in a large class of 1D non-Hermitian
quasiperiodic models with parity-time ($\mathcal{PT}$) symmetry. We illustrate
our method by studying a specific model. We first use our method to determine
the energy-dependent mobility edge as well as the spectrum for localized
eigenstates in this model. We then demonstrate that the metal-insulator
transition must occur simultaneously with the spontaneous
$\mathcal{PT}$-symmetry breaking transition in this model. Finally, we propose
an experimental protocol based on a 1D photonic lattice to distinguish the
extended and localized single-particle states in our model.
