The invention provides a data access method of a memory device. In one embodiment, the memory device comprises a plurality of memories. First, a plurality of commands sequentially received from a host is stored in a command queue. A target command is then retrieved from the command queue. A target memory accessed by the target command is then determined. Whether the target memory is in a busy state is then determined. When the target memory is not in a busy state, access operations requested by the target command are then performed. When the target memory is in a busy state, a substitute command is selected from a plurality of subsequent commands stored in the command queue and access operations requested by the substitute command are performed, wherein the sequence of the subsequent commands in the command queue is subsequent to the target command.