An operation method of a nonvolatile memory device includes receiving a read command and an address, increasing a voltage applied to an unselected word line from an off voltage to a read pass voltage during a setup phase in response to the read command, increasing a voltage applied to an unselected string selection line from the off voltage to a pre-pulse voltage during a first setup phase of the setup phase, increasing a voltage applied to an unselected ground selection line from the off voltage to the pre-pulse voltage during the first setup phase, applying a read voltage to a selected word line to read data corresponding to the address, during a sensing phase following the setup phase, and outputting the read data through data lines after the sensing phase. During the setup phase, a slope of the voltage applied to the unselected word line is varied.