I have found the reason what caused this problem, just missing "\n" after the row of the AppleScript code. Below code is success:
NSString *strScriptUnload = [NSString stringWithFormat:@"\
set UserName to \"%@\"\n\
set MyPASSWORD to \"%@\"\n\
do shell script \"sudo kextunload /System/Library/Extensions/FTDIUSBSerialDriver.kext\" user name UserName password MyPASSWORD with administrator privileges\n\
do shell script \"sudo cp ./libftd2xx.1.0.2.dylib /usr/local/lib\" user name UserName password MyPASSWORD with administrator privileges\n\
do shell script \"sudo cp ./libd2xx_table.dylib /usr/local/lib\" user name UserName password MyPASSWORD with administrator privileges\n\
do shell script \"cd /usr/local/lib\" user name UserName password MyPASSWORD with administrator privileges\n\
do shell script \"sudo ln -sf libftd2xx.1.0.2.dylib libftd2xx.dylib\" user name UserName password MyPASSWORD with administrator privileges\n",[m_textUserName stringValue], [m_textPassword stringValue]];
NSAppleScript *appUnloadScript = [[NSAppleScript alloc] initWithSource:strScriptUnload];
returnDescriptor = [appUnloadScript executeAndReturnError:nil];
[appUnloadScript release];
Thanks all!