  The decoding throughput in the postprocessing is one of the bottlenecks for a
continuous-variable quantum key distribution (CV-QKD) system. In this paper, we
propose a layered decoder to decode quasi-cyclic multi-edge type LDPC
(QC-METLDPC) codes based on graphic processing unit (GPU) in
continuous-variable quantum key distribution (CV-QKD) systems. We optimize the
storage method of the parity check matrix, merge the sub-matrices which are
unrelated, and decode multiple codewords in parallel on GPU. Simulation results
demonstrate that the average decoding speed of LDPC codes with three typical
code rates, i.e., 0.1, 0.05 and 0.02, is up to 64.11Mbits/s, 48.65Mbits/s and
39.51Mbits/s, respectively, when decoding 128 codewords of length 106
simultaneously without early termination.
