A memory system includes: nonvolatile memory devices and a memory controller confirming a programming time for each word line of each of the nonvolatile memory devices and calculating a target programming time on the basis of the programming time for each word line. Each of the nonvolatile memory devices receives the target programming time from the memory controller, and adjusts the programming time for each word line on the basis of the target programming time. When the adjustment of the programming time for each word line is completed, the memory controller confirms a variation width of a writing speed of the memory system for a predetermined time, and sets the target programming time as a final target programming time when the variation width of the writing speed is smaller than a reference value.