A data storage device is provided. The data storage device includes a flash memory and a controller. The flash memory stores a firmware that includes a plurality of mode page settings, and each mode page setting includes a plurality of mode parameters. The controller receives a data out message arranged to rewrite a first mode page setting among the plurality of mode page settings from a host. The controller determines whether the data out message will change the mode parameters which cannot be rewritten in the first mode page setting by performing bitwise logic operations on a new mode page setting in the data out message, preset values of the plurality of mode parameters of the first mode page setting, and a rewriteable setting for each bit of the first mode page setting.