Thanks for reply.

In fact, I read the datasheet, but somehow it just different from the real world. Anyway, just burn 1 because I plugged in the wrong cable which power up the LCD with 10 volts.

The contrast, indeed need negative voltage of up to -5.7 vdc with relative
to 0/gnd. Whereas the Vdd remain at 5.1 Vdc.

The LCD is made by OPTREX model DMC20481.