Abstract: Drilling relief well is an effective way to control blowout at present. To study electromagnetic detection for relief wells, by using well-ground current injection method, the relief well detection model based on point source has been built, finite element software has been used to analyze impacts of electrode arrangement, current size, the distance between blowout well and electrode, and casing length on density of aggregation current on casing in the well with incident. The research results show installation of ground electrodes on casing may facilitate current aggregation on casing of well with incident; the longer the distance between electrode and casing, the lower the density of aggregation current will be, in addition, the in-flow current and density of aggregation current on casing are in linear relationship; density of aggregation current increases with increase of casing length, but amplitude of such increase decreases with the increase of casing length. Relevant researches have verified effectiveness and applicability of the model for aggregation current on casing in wells with incident. The research results can provide a theoretical basis for developing tools detecting connectivity with the relief well.