Abstract: A 1D inversion code is developed for the loop-source transient electromagnetic method (TEM) based on the open-source code Dipole1D and Occam's algorithm. This code is tested by a four-layer stratified model. Then, the model with a tilted earth-air interface is considered, for which the synthetic data are calculated by 3D finite-element method. The inversion results show that 1D inversion can be directly used for the scenario with tilted interface. Finally, this 1D inversion code is used for a field case, in which TEM is employed to delineate the 3D distributed domains of a basalt which intruded into shale and sandstone. The inversion result shows that the thickness of the basalt coincides with the drilling data, and the shape of the basalt like a pot bottom.