Laser-induced breakdown spectroscopy (LIBS) is a practical technique for in-situ detection, but self-absorption effect has been a big issue for quantitative applications of this technique. In presented work, a method was developed to correct self-absorption to improve the quantitation of underwater LIBS. We proposed "relative self-absorption coefficient" as the critical parameter to evaluate self-absorption, and the plasma image was employed as the reference to determine the coefficient value. Based on that, the LIBS detection was successfully corrected by the coefficient to realize quantitative analysis, and the "Dominant Factor-PLS" was used as assistance. The results indicated that our method greatly improved LIBS quantitation in practice. More importantly, the calibration curve was able to be established with high linearity (R2 = 0.9999) to cover a large concentration range (0–103 ppm). It is hoped that our method could be a contribution to developing LIBS as an analytical tool for field measurements. [Display omitted] ∙Relative self-absorption coefficient is a useful parameter to evaluate the self-absorption situation without considering the theoretical intensity; ∙Plasma image is a direct way to show the self-absorption effect; ∙Self-absorption effect is effectively corrected by using plasma images and relative self-absorption coefficient; ∙Calibration curve could be established with high linearity (R2 = 0.9999) in a large concentration range (0–103 ppm). [ABSTRACT FROM AUTHOR]