The REST operation for multilevel storage in phase change random access memory cell is investigated via numerical simulation. A three-dimensional memory cell model is built, and the physical property variation is calculated by solving the Laplace equation and the heat conduction equation with finite element method. The phase distribution in phase change layer and the total resistance of the cell are examined. The influences of cell structure size variation on multilevel storage process and states are analyzed. The simulation results demonstrate that multilevel storage can be achieved through accurate electrical pulse control while the variations of phase change layer thickness and bottom electrode contact size have relatively large effect on the storage state. The storage states can all keep stable for more than 10 years at 80 ℃.