The　packet　loss　problem　seriously　affects　the　quality　of　service　in　Voice　over　IP　(VoIP)　sceneries.　In　this　paper,　we　investigated　receiver-based　packet　loss　concealment　which　is　much　more　portable　and　applicable　compared　with　sender-based　methods.　For　ensuring　the　speech　naturalness,　rather　than　directly　processing　time-domain　waveforms　or　separately　reconstructing　amplitudes　and　phases　in　frequency　domain,　a　flow-based　neural　vocoder　is　adopted　to　generate　the　substitution　waveform　of　lost　packet　from　Mel-spectrogram　which　is　generated　from　history　contents　by　a　well-designed　neural　predictor.　Furthermore,　a　waveform　similarity-based　smoothing　post-process　is　created　to　mitigate　the　discontinuity　of　speech　and　avoid　the　artifacts.　The　experimental　results　show　the　outstanding　performance　of　the　proposed　method.　　©　2022　IEEE.