In this paper,several mothocis of impedance computation in non-uniform medium are analysed.lt is emphatically discussed to-use the Generalise Inverse Matrix Mothod in impedance Computation,to use the Information Matix to suppress cohereut noise and to define judgement indicator to measure the Level of coherent noise.At Last,the author poiuts out the saetteomiugs of various mothods and their improverrieuts.