A capacitive voltage mutual inductor (2) for a transient over-voltage monitoring system comprises a first capacitor (C1), a second capacitor (C2), a third capacitor (C3), an intermediate transformer (T), a transient over-voltage monitoring unit (M), a grounding switch (K), a compensation reactor (L) and a first lightning arrester (BL1). One end of the first capacitor (C1) is connected to a power grid (1), and the other end is respectively connected to one end of the second capacitor (C2) and one end of a primary winding in the intermediate transformer (T). The other end of the second capacitor (C2) is respectively connected to one end of the transient over-voltage monitoring unit (M) and one end of the compensation reactor (L). The other end of the primary winding of the intermediate transformer (T) is respectively connected to the other end of the compensation reactor (L) and one end of the first lightning arrester (BL1). The other end of the transient over-voltage monitoring unit (M) and the other end of the first lightning arrester (BL1) are both grounded. The grounding switch (K) is connected in parallel at the two ends of the transient over-voltage monitoring unit (M). One end of the third capacitor (C3) is connected to the other end of the second capacitor (C2), and the other end of the third capacitor (C3) is grounded. A voltage bearable by the first capacitor (C1) is greater than a voltage bearable by the second capacitor (C2), and the voltage bearable by the second capacitor (C2) is greater than a voltage bearable by the third capacitor (C3).