The precise load shedding of source-grid-load friendly interaction system can realize accurate control of the interruptible load on the user side when UHV DC fault occurs through classified management of user side load. Compared with the traditional way of integral power cut-off, it can greatly reduce the social impact caused by faults. This paper analyzes the control requirements of the load shedding system, establishes the load classification model based on the precise load shedding system, discusses the load selection algorithm, and proposes a load selection method for load shedding margin optimization based on the basic load selection (BLS) algorithm. The simulation on the algorithm shows that the method effectively optimizes the allowable load shedding of the system and achieves the requirement of the precise load shedding.