中文摘要：

可控源音频大地电磁法在资源勘探等领域中发挥着重要的作用．我们把有限差分数值模拟方法用于可控源音频大地电磁三维正演，结合正则化反演方案和共轭梯度反演的思路，将反演中的雅可比矩阵计算问题转为求解两次“拟正演”问题，得到模型参数的更新步长，形成反演迭代，实现了可控源音频大地电磁三维共轭梯度反演算法．该反演算法可用于对有限长度电偶源激发下采集到的可控源音频大地电磁全区（近区、过渡区和远区）视电阻率和相位资料进行三维反演定量解释，获得地下三维模型的电阻率结构．理论模型合成数据的反演算例验证了所实现的可控源音频大地电磁三维共轭梯度反演算法的有效性和稳定性．

英文摘要：

CSAMT plays an important role in the field of resource exploration and so on. This work applies the finite difference method to the CSAMT forward modeling. We develop a three- dimensional （3D） conjugate gradient inversion algorithm for inverting CSAMT data using the regularized solution and conjugate gradient inversion method. In the inversion, the computation of Jacobian matrix is replaced by two-time ＂pseudo-forward＂ problem solution to make the model updated directly. This algorithm is suitable for inverting CSAMT in the entire field （near field, transition zone and far field） data to obtain 3D geoelectrical structure underground. The synthetic example demonstrates the validity and stability of the 3D conjugate gradient inversion algorithm presented in this paper.