This paper proposed a method of voltage sag frequency estimation considering multiple PCC points based on area of severity concept. Exposed areas of multiple PCC points are determined based on analytical approach. Then buses and lines are graded into different areas of severity according to the intersection of exposed areas. The severity of buses and lines is ranked considering sag frequencies of multiple PCC points caused by faults in the different areas of severity, and the contribution degree to the total frequencies of faults in each bus or line. Case study for IEEE-14 bus test system confirms its validity and feasibility and proves that different measures should be taken to lines with different severity in order to reduce spending of suppressing sags.