A memory storage device including a memory storage array and a memory controller is provided. The memory storage array is configured to store data. The memory controller is coupled to the memory storage array. The memory controller is configured to write to-be-written data to the memory storage array. The to-be-written data includes a plurality of data bits and a flip bit. The memory controller performs a verification operation on the to-be-written data to determine whether the data bits includes error bits and records information of the error bits. The memory controller, determines, according to a quantity of the error bits, whether to invert parities of the data bits and the flip bit, and records the parity of the flip bit. In addition, a data access method is also provided.