Abstract: Using a double-coiled rectangle cross section of cylinder mutual-inductive sensor as seam-tracking sensor, the tracking of steel sheet lapping was realized. The mutual-inductance coefficient of the axes-intersecting coils was calculated with the cycle loop method. A 3D model was built for the sensor through Ansys software. After optimizing the parameters of the coils and analyzing the influence of the angle between coils on the output of sensor, the structure of mutual-inductive sensor was defined for seam tracking. The experimental results show that the linearity of sensor output was fine and the tracking precision fulfilled the requirements. This research provides a new way for automatic seam-tracking of lapping sheet.