Voltage sag is the most severe power quality issue. Therefore, it is highly significant to determine the precise location of the voltage sag source for subsequent management and improvement of power quality. The traditional optimal configuration of monitoring points for sag source location has a disadvantage: the number of monitoring points needs a continuous increase to rectify the ambiguous region of monitoring point positioning, resulting in a complicated correction process and a large number of installed monitoring points. To address this issue, this paper proposes a method for optimizing monitoring points in voltage sag source location. Firstly, the fault types are determined, and the fault distances under different fault types are calculated. Then, the lines that satisfy the requirements are added to the set of possible fault lines. Next, the combination of monitoring points containing the fewest number of lines from the set of possible fault lines is selected as the final configuration scheme for monitoring points. Finally, the proposed method is validated through simulation using the IEEE-39 node standard system.