Three times of magnetotelluric measurements were carried out during loading and unloading of the Longtan reservoir in Guangxi from 2009 to early 2010. The surveys were conducted at 4 sites with a frequency band 320 Hz～1 000 s. The results show that the electricity of deep subsurface changed in different manners during the loading and unloading of the reservoir, depending on the specific structures and rock properties. These measurements also indicate that at different stages of loading and unloading of the reservoir, the rock properties, area of the reservoir and change of reservoir weight can pose a major influence on interconnection and seepage of underground water, causing variations of electricity of the subsurface at a certain depth.oft-com:office:office" />