The invention discloses a power frequency electric field intensity monitoring system for a power transmission and transformation project. The system comprises a sensor, a signal transmission line, a display device and a bracket. The sensor is connected with the display device through the signal transmission line. The sensor is fixed on the bracket. The capacitance of the bracket is less than 0.5 pF. The equivalent resistance of the bracket is greater than 50 G ohm. The power frequency electric field intensity monitoring system has the advantages of small error and accurate monitoring result.