On the basis of a discussion on the source of magnetotelluric field,this paper points out that the noises affecting magnetotelluric sounding data can be divided into field source noise,geological noise and human noise,which are derived from different sources.The authors studied the influences of various sorts of noises upon the magnetotelluric sounding data and made frequency spectrum analysis for several sorts of common noise interferences.The geological noise commonly affects the whole frequency domain,and the near field interference mainly affects the limited frequency of high frequency.Nevertheless,the nearby thunder and lightning affect relatively wide frequency band of the high frequency,whereas the unstability of the load system mainly affects the low frequency.Finally,some suggestions are made concerning the elimination or reduction of various noise interferences.