A data protection method applied to a data storage device including a volatile memory and a non-volatile flash memory is provided. The data protection method includes, executing a protection program after the data storage device is coupled to a host, to perform following steps: shielding a refresh command from the host; monitoring a working voltage of the data storage device through a voltage sensing module; determining whether the working voltage is lower than a threshold; when it is determined that the working voltage is lower than the threshold, providing the data storage device with power to trigger the refresh command to write the data in the volatile memory into the non-volatile flash memory. Therefore, the writing times of the data storage device are reduced, the performance degradation of the data storage device is avoided, and the service life of the data storage device is extended.