  Mode-pairing quantum key distribution (MP-QKD) can surpass the repeaterless
rate-transmittance bound (Pirandola-Laurenza-Ottaviani-Banchi bound) without
requiring global phase locking, exhibiting remarkable flexibility. However,
MP-QKD necessitates equal communication distances in two channels, which is a
challenging requirement in practical applications. To address this limitation,
we extend the original MP-QKD to asymmetric cases. Our decoy-state estimation
confirms that asymmetric channel transmittances and asymmetric intensities do
not compromise the security of the protocol. We focus on the pulse-intensity
relationship, a key factor for optimizing the performance of asymmetric MP-QKD.
Unlike previous asymmetric protocols, the intensities of different bases in
asymmetric MP-QKD cannot be decoupled. We introduce an optimal-pulse-intensity
method, adaptable to various scenarios, to enhance key rates by calculating
ideal pulse intensities. Simulation results in various representative scenarios
indicate that our method effectively reduces the impact of asymmetric channel
distances on MP-QKD performance, enhancing its practical applicability.
