This technology relates to a method and apparatus for improving I/O throughput through an interleaving operation for multiple memory dies of a memory system. A memory system may include: multiple memory dies suitable for outputting data of different sizes in response to a read request; and a controller in communication with the multiple memory dies through multiple channels, and suitable for: performing a correlation operation on the read request so that the multiple memory dies interleave and output target data corresponding to the read request through the multiple channels, determining a pending credit using a result of the correlation operation, and reading, from the multiple memory dies, the target data corresponding to the read request and additional data stored in a same storage unit as the target data, based on a type of the target data corresponding to the read request and the pending credit.