Abstract: In the field work of control一source magnetotelluric method,the space between the transmitter and the receiver is more than 3~5 times skin depth,so it is important to study the impact of the abnormal body in this area on the target body in the exploration area. In this paper, to a line source,the impact of the abnormal body out of exploration area with different resistivity,size and location on the target body in the exploration area is discussed with 2D finite element method(FEM ).Through the study,it can be concluded that if the abnormal body out of the exploration area is a conductor,the lower the resistivity,the larger the impact on the exploration area;the larger its size,the larger the impact;the shallower its buried,the larger the impact range;the deeper its buried depth,the smaller the impact on the body in the shallow exploration area,but its impact is almost same as what the shallow one has. When the abnormal body is resistive,the similar effect rules can be obtained,but the impact is very small.