Source effects have serious impact on the application effect of CSAMT. In order to analyze the effect of the source effects, the authors used three-dimensional integral equation numerical simulation method to simulate 3D anomalous body below the source, and then made a field test. Simulations and field tests have proved that, due to the different depths of the bedrocks, only the low band is affected, whereas the high band is almost unaffected, and that the low resistivity body can generate stronger source overprint effects, so the observational data are more remarkably impacted by the low resistivity body.