Thanks for your reply,It's not just the difference in values, the two results sound quite different. I tested the PESQ-WB, the website is 1.777, and my own is 1.319. My own decoding results sound a lot of glitches.

PESQ.exe +16000 +wb ref.pcm ref_dec.pcm
PESQ.exe +16000 +wb ref.pcm lpcnq.pcm

I don't know if it is because of my compile, because a lot of warnings are generated, such as:

In file included from src/lpcnet_dec.c:38:0:
src/pitch.h:37:1: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
//#include "modes.h"
^
src/pitch.h:37:1: warning: (this will be reported only once per input file) [enabled by default]
src/lpcnet_dec.c: In function 'decode_packet':
src/lpcnet_dec.c:96:3: warning: ISO C90 forbids mixed declarations and code [-Wpedantic]
unpacker bits;
^
src/lpcnet_dec.c:108:3: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
//fprintf(stdout, "%d %d %d %d %d %d %d %d %d\n", c0_id, main_pitch, modulation, corr_id, vq_end[0], vq_end[1], vq_end[2], vq_mid, interp_id);
^
src/lpcnet_dec.c:108:3: warning: (this will be reported only once per input file) [enabled by default]
src/lpcnet_dec.c:135:3: warning: ISO C90 forbids mixed declarations and code [-Wpedantic]
float sign = 1;
^
CC src/lpcnet_enc.lo
In file included from src/lpcnet_enc.c:38:0:
src/pitch.h:37:1: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
//#include "modes.h"
^
src/pitch.h:37:1: warning: (this will be reported only once per input file) [enabled by default]
src/lpcnet_enc.c:46:1: warning: C++ style comments are not allowed in ISO C90 [enabled by default]
//#define NB_FEATURES (2*NB_BANDS+3+LPC_ORDER)

PS:
The voice bandwidth of the "MELP 2.4kbps" downloaded from the website is 4kHz, but the MELP 2.4kbps program I downloaded from the network generates a voice bandwidth of 8kHz.