A system and a method for writing cache data and a system and a method for reading cache data are disclosed. The system for writing the cache data includes: an on-chip memory device, configured to cache received write requests and write data associated with the write requests and sort the write requests; a request judging device, configured to extract the sorted write requests and the write data associated with the write requests according to write time sequence restriction information of an off-chip memory device; and an off-chip memory device controller, configured to write the write data extracted by the request judging device in the off-chip memory device.