Hi!
Thanks for your help.
We have found out how this issue come from.
In CW5.1 IDE, the default prm file as below.

,but the Mcu02e9.fpp file in CWS12v5.1\Prog\fpp is like below.

And we don't know why this happens.
As we replace this file as in CW4.7 in CWS12v4.7\Prog\fpp is like below,

Things turns to be OK. As we download the same program to the mcu, we read the correct value .