In order to improve the efficiency of substation electromagnetic environment information collection and the accuracy of data measurement, an intelligent mobile monitoring device is designed and manufactured in this paper. Self-designed power frequency electric field probe can realize synchronous measurement of power frequency electric field in three directions. The power frequency magnetic field acquisition circuit with reset circuit can eliminate the abnormal problem caused by the interference of strong magnetic field to the magneto-resistive sensor. External temperature and humidity module are installed to ensure the accuracy of measurement. When the humidity is less than 70%, the measurement error is within 5%. The third-party test results show that the error of electromagnetic field measurement results is within 5%. The electromagnetic environment measuring results in actual 110 kV substation indicate that, this device can walk and measure accurately following the specified path. A three-dimensional model is established to simulate the spatial electromagnetic field distribution. The measured data and simulation data achieve the same change trend, which further verifies the measuring accuracy of the device.