Abstract: The X-ray profile gauge for hot steel strip gets two projections of the cross-section in the steel strip using two Xray sources and two arrays of gas-filled ionization chambers. Combining the information of the relative positions of the two X-ray sources and the two arrays of detectors, the information about the surface of the hot steel strip and the thickness information provided by the two projections of the cross-section, the two edges of the cross-section were computed successfully and the thickness distribution of the cross-section was reconstructed. The algorithm provided here has been used successfully in the gauge.