Abstract: Two-dimensional(2D) or three-dimensional(3D) forward modeling is a challenge for geometrically complex magnetotelluric(MT) problems.To solve the complex 2D/3D MT forward problems,we apply the finite element method.The finite element method is used to form a linear equation,and the coefficient matrix is a large sparse,banded,symmetric,conditioned,complex matrix.Its condition number is far larger than 1,and it is an ill-conditioned matrix.Solving large scale ill-conditioned linear equation is very difficult.The Bi-CGSTAB algorithm with incomplete LU decomposition for preconditioning could be used to solve this system linear equation,with advantages of high speed,high precision and stability;In order to simulate the infinity border and meet the demand computer memory,the non-uniform gird is designed with ensuring the accuracy;In programming,we only store the non-zero elements of the finite element matrix.By numerical simulation of 2D/3D MT responses,we verified the correctness of the magnetotelluric forward method.