In the event of a serious disaster， every effort should be made to ensure power supply to vital end users. Differential planning is an important stage of constructing the smart grid， through which the design standards for part of the components should be so raised that they can bear more serious disasters than the other components. The guiding principles of differential planning are proposed and a new level of power load would be added， defined as the special grade load， which should be moderately centralized. By adopting the special grade grid， the grid can be minimized with higher standards. It is proposed that two levels of differential planning be worked out， one for the special grade load， and the other for the levelⅠ load. The optimization model for differential planning is analyzed and its procedure is given.