The invention relates to a nanosecond impulse voltage generator and a detection system for detecting overvoltage of a mutual inductor. The nanosecond impulse voltage generator includes a high-frequency high-voltage pulse power supply, an energy storage capacitor, a pulse forming switch, a steepening device and a high-voltage terminal, wherein the high-frequency high-voltage pulse power supply andthe energy storage capacitor are connected in series to form an integrated structure; the pulse forming switch is connected with the high-voltage terminal through the steepening device to form a branch circuit; the two ends of the branch circuit are connected in parallel at the two ends of the energy storage capacitor. The nanosecond impulse voltage generator and the detection system are beneficial to miniaturization, low in cost and high in detection reliability.