Real-time determination of formation boundary is one of the key problems in  geological directional drilling of horizontal wells. Considering mud resistivity and borehole have less effect on LWD electromagnetic wave in a certain range, 3D formation model was simplified as 1D formation model, the forward computation time can be reduced greatly. The distances between instrument and formation boundary are reconstructed using the real time inversion of Marquand method. The result shows that computed location agree can be controlled, it can maintain the borehole in a desired geological bed, and further improves the capability of geo-steering in horizontal wells.