Like other geophysical inversions, gravity and magnetic inversions can produce severe ambiguous solutions. Therefore, special constraints must be introduced in the process of inversion so as to obtain a unique and stable interpretation. In3Dcase, the situation is worse in that the solution is more ambiguous and the combination of constraints is more difficult. The application of nonlinear inversion makes the interpretation more stable and the introduction of constraints easier than previous linear methods. In addition, the difficulties caused by nonlinear methods, such as the high dimensional searching and the low computation speed, can be tackled and well solved by special pertinent skills. After improvement the application of 3Dinversion will surely be more practical than before.