Abstract: Electromagnetic environment monitoring is an important topic of environmental protection in power transmission and distribution projects. In view of the problem that the widely used electric field monitoring instruments can’t realize the power frequency electric field measurement under the condition of environmental humidity greater than 80%,firstly,the principles of two basic power frequency electric field measurements are discussed,which is optical measurement method and electrical measurement method,and the basic principles and measurement methods of the floating electric field probe and the ground-referenced electric field probe are compared and analyzed. Secondly,by analyzing the influence of humidity on electric field monitoring instruments,a power frequency electromagnetic field measurement system based on ground-referenced probes under high humidity conditions is constructed.Thirdly,a comparative test and data analysis were carried out on the selected test circuit under different environmental humidity conditions. The test results show that air humidity basically has no effect on the distribution of power frequency electric field.The measurement system constructed in this paper can monitor the electric field strength under high humidity conditions,and can provide strong technical support for electromagnetic environment measurement in rainy or humid weather.