Embodiments of the present disclosure relate to the technical field of semiconductors and provide a storage system and a data writing method thereof. The storage system is configured to: enter a write data copy mode in response to a write-copy enable signal; if at least two groups of data in multiple groups of data exported from multiple data ports are a same in the write data copy mode, define the at least two groups of data as a category; generate an identification signal that is used to indicate a data copy; transmit one group of data in the category to an interface of a memory array; and disconnect a transmission path between a data port corresponding to another group of data in the category and another interface of the memory array, wherein the memory array, in response to the write-copy enable signal and the identification signal.