An on-line monitoring device based on two-stage subdivision for overvoltages in 35kV grid is presented. A low damped capacitive divider is designed as an overvoltage sensor in the first subdivision. The device can be applied to 10kV to 35kV distribution grid while changing the second voltage division ratio. A high damped capacitive divider is designed as the second subdivision. The divider’s designing methods and response characteristics are analyzed. The power frequency ratio is in accordance with the impulse ratio, which can meet the requirement of the internal and external overvoltage monitoring. Moreover, with the data double buffering and high-speed sampling techniques, this device can collect longer data (64 Mbytes) and shorten interval time (less than 1 s) at a high sampling rate (up to 20 MHz). The result of the measurement indicates that the device has good precision and can monitor internal and lightning overvoltages at a qualified precision.