Abstract: Based on diurnal electric field data of four stations of Jiangsu Province,combined with horizontal component of geomagnetic field and line tidal strain theory,this paper studies the characteristic of the diurnal variation and differences of the electric field.The result shows that:(1) the amplitude of semi daily wave is the biggest followed by the 1/4 daily wave;(2) Diurnal variation of electric field is affected by magnetic field and tidal.The electric field of the stations near the sea and lake are obviously affected by earth tide while the electric field of the stations away from the river,sea and lake are more related to the horizontal component of the geomagnetic daily variation,the differences between them are affected by the location of stations and the electrical structures.