The invention discloses an IO processing method in a storage system, which comprises the following steps: merging data of overlapping IO in a chain list to form merged data; Performing a down brush operation on the merged data; After brushing the merged data, the corresponding response function is called to complete the IO processing. The method fully utilizes the existing linked list of overlapping IO, merges the data of overlapping IO in the linked list first, and then performs down-brush operation on the merged data, that is to say, merges the data of overlapping IO in advance, so that themerged data can be brushed down once and returned in batch; Further, the number of reads and writes to the back-end disk can be reduced, the delay of IO processing can be reduced, and the IOPS of thestorage device can be improved as a whole; The invention also discloses an IO processing device, a terminal and a computer-readable storage medium in a storage system, which have the beneficial effects mentioned above.