An operating method of a storage device is provided. The operating method comprises the following steps. First, a first data is read from a target address of a first storage unit. Then, an assisting unit checks whether the target address is corresponding to a second data stored in a second storage unit. If the target address is corresponding to the second data, the assisting unit updates the first data according to the second data to generate an updated data. Next, an Error Correction Code (ECC) performs a decoding process on the updated data to generate a decoded data.