A method for preventing a data storage device from data shift errors is provided. First, data is encoded into an error correction code. The error correction code is then scrambled to obtain a scrambled code to be stored in a memory. The scrambled code is then retrieved from the memory to obtain first read-out data. The first read-out data is then descrambled to obtain a first descrambled error correction code. The first descrambled error correction code is then decoded to determine whether the first descrambled error correction code has uncorrectable errors. When the first descrambled error correction code has uncorrectable errors, the scrambled code stored in the memory is read again to output second read-out data without shift errors. Following, the second read-out data is then descrambled to obtain a second descrambled error correction code, and the second descrambled error correction code is then decoded to recover the data.