An identification technique for physically damaged blocks of a flash memory of a data storage device. In the data storage device, a controller coupled to the flash memory writes data into the flash memory with at least one time stamp corresponding to the data. The time stamp is taken into consideration by the controller to identify the physically damaged blocks of the flash memory, and thereby it is prevented from erroneously identifying a physically undamaged block as bad. Thus, the flash memory is prevented from being erroneously regarded as a write protected memory. The lifespan of the flash memory is effectively prolonged.