The electromagnetic noise sources in the Dongguanshan ore district were investigated in this paper, and the five-component electromagnetic field was measured along the test profile with spectrum analyzer. According to test results, the electromagnetic noise is mainly composed of 50 Hz and its odd harmonics, and the even harmonics is also strong at some sites; the harmonic number of noise is related to the intensity of noise; not only the electromagnetic noise characteristics are different from each other at different sites, but also the noise characteristics of each component are different. Except for the regular noise, there exists ambient broad banded noise, which occurs at all the frequency band, with stable amplitude. The result of long time noise measurement shows that there is not any weak-noise time interval in this ore district.