In order to reasonably divide the microgrid topology and accurately determine the fault area under various microgrid faults, a fault area determination technology of grid connected photovoltaic microgrid in 4D coordinate system is proposed. The microgrid topology is taken as a constellation diagram and the equipment nodes are selected as constellation points. On the basis of maximizing the minimum Euclidean distance between constellation points and minimizing the number of average nearest neighbor constellation points, using the set division method of ball filling 4D constellation point set to divide the microgrid topology and obtain the microgrid division area. Taking each divided area as the node and the circuit breaker as the edge, the microgrid fault mathematical model is constructed by graph theory algorithm. According to the power change before and after the fault and the direction of regional fault current, the fault area judgment matrix is established to realize the fault area judgment. The experiments show that this technology can effectively divide the microgrid topology and improve the signal transmission effect of microgrid. In case of multiple faults, twophase faults and system side faults, the technology can accurately determine the fault area.