On the basis of magnetotelluric sounding practice in northwestern China since many years, arrangement condition of observation point is discussed from observation instrument, topography and interference factor. The arrangement pattern of electrode in field observation is analysed. Analysing the difference between observation data in mountain area and that in basin, some suggestions on arrangement condition of the observation points are made. The data disturbed by electromagnetic noises of two observation points are showed. Observing effect at the point which is reselected distant from interference source is better. It is considered if frequency of interference signal is close to that of magnetotelluric sounding signal, it will be difficult for instrument to restrain the interferences by oneself because resistance of the instrument to interferences is limited.