The content of molybdenum （Mo） element in alloy structural steel has significant effects on its performance， making the detection of Mo content in alloy structural steel of great significance. However， the spectral interference and self-absorption effects of matrix element （Fe） in alloy structural steel severely affect the accuracy of laser-induced breakdown spectroscopy （LIBS） for quantitative analysis of Mo element. In this work， we employed laser-induced fluorescence-assisted laser-induced breakdown spectroscopy （LIBS-LIF） to address these issues. We selected three spectral lines， Mo I 379.83 nm， Mo I 386.41 nm， and Mo I 390.30 nm， as the analysis lines. The results showed that LIBS-LIF enhanced the spectral intensities of the three analysis lines， eliminating spectral interferences. As the Mo content increased from 0.019 wt. % to 1.4 wt. %， the spectral intensities of Mo element lines also significantly increased. Compared to the traditional LIBS technique， the self-absorption factor of the Mo I 386.41 nm line decreased by 99.99% in LIBS-LIF， the root mean square error of cross-validation decreased by 65.37%， the average relative deviation decreased by 85.69%， and the average relative standard deviation decreased by 20.20%. Therefore， LIBS-LIF can effectively reduce spectral interferences and self-absorption effects， improving the accuracy of quantitative analysis.