  Reference-frame-independent measurement-device-independent quantum key
distribution (RFI-MDI-QKD) is a novel protocol which eliminates all possible
attacks on detector side and necessity of reference-frame alignment in source
sides. However, its performance may degrade notably due to statistical
fluctuations, since more parameters, e.g. yields and error rates for
mismatched-basis events, must be accumulated to monitor the security. In this
work, we find that the original decoy-states method estimates these yields over
pessimistically since it ignores the potential relations between different
bases. Through processing parameters of different bases jointly, the
performance of RFI-MDI-QKD is greatly improved in terms of secret key rate and
achievable distance when statistical fluctuations are considered. Our results
pave an avenue towards practical RFI-MDI-QKD.
