  The value of residual phase noise, after phase compensation, is one of the
key limitations of performance improvement for continuous-variable quantum key
distribution using a local local oscillator (LLO CV-QKD) system, since it is
the major excess noise. However, due to the non-ideality of the realistic
devices implemented in practice, for example, imperfect lasers, detectors and
unbalanced interferometers, the value of residual phase noise in current system
is still relatively large. Here, we develop a phase noise model to improve the
phase noise tolerance of the LLO CV-QKD schemes. In our model, part of the
phase-reference measurement noise associated with detection efficiency and
electronic noise of Bob's detector as well as a real-time monitored
phasereference intensity at Bob's side is considered trusted because it can be
locally calibrated by Bob. We show that using our phase noise model can
significantly improve the secure key rate and transmission distance of the LLO
CV-QKD system. We further conduct an experiment to substantiate the superiority
of the phase noise model. Based on experimental data of a LLO CV-QKD system in
the 25 km optical fiber channel, we demonstrate that the secure key rate under
our phase noise model is approximately 40% higher than that under the
conventional phase noise model.

Quantum Physics