In this paper，the abnormal variations of geoelectric field observed at three stations in the Shanghai area are studied by the principle of multi-dipole observation system of geoelectric field，and the different types of interference of geoelectric field are distinguished． The results show that the multi-dipole observation system of geoelectric field and the analysis method can effectively recognize the abnormal signal of Electrode polarization interference， Lightning interference，HVDC transmission interference， ionospheric disturbances， and abnormities of spontaneous electric field．