The utility model discloses a transient overvoltage real-time monitoring device for a fixed transformer substation. The system comprises a local acquisition end, the local acquisition end is connectedwith a cloud server in a wireless mode, the local acquisition end comprises a signal acquisition front end and a data processing rear end, the signal acquisition front end and the data processing rear end are connected through a polarization maintaining optical fiber, and the data processing rear end is arranged in a fixed cabinet. The signal acquisition front end comprises an insulation supporting rod and a probe. The probe comprises an upper shell, a lower shell, an integrated optical sensor, an installation clamping groove and an optical fiber coupler. The data processing rear end comprises an optical signal processing module, an electric signal collecting and processing module, a GPS module, a communication module, a voltage measuring module and a temperature control module. Accordingto the utility model, the time precision of transient data is improved, the voltage measurement module is used for measuring CVT signals, the decoupling difficulty is reduced, the GPS module is usedfor improving the timing precision, the communication module is used for wireless transmission, and the real-time performance of monitoring is improved.