The technology of aluminum alloy welding is widely used in industrial production, manufacturing and maintenance. Porosity in welding seam leads to the decrease of welding quality, which is a common problem in aluminum alloy welding technology. The metal oxide on the surface of aluminum alloy is the main source of pore formation, therefore, on-line detection of laser cleaning process can analyze the cleaning status of surface oxides in real time and avoid damage or secondary oxidation of matrix surface caused by excessive cleaning at the same time. In this paper, laser-induced breakdown spectroscopy (LIBS) was used to detect the laser cleaning process of aluminum alloy before welding and to characterize the surface state of aluminum alloy after cleaning. LIBS technology can simultaneously detect multi-element components, with a lower detection limit and higher accuracy. In this paper, an on-line detection system for laser cleaning of aluminum alloy before welding based on AdorMechelle 5000 spectrometer was built, eliminated the influence of air environment on the experimental results, the LIBS spectra of 6061 aluminum alloy surface oxide and aluminum alloy matrix were measured, analyzed their elemental characteristic spectra, verified the accuracy of elemental characteristic spectra by using EDS test results, and explored the feasibility of LIBS technology in on-line detection of laser cleaning process. The relationship between spectral line intensity of plasma and laser energy density was tested experimentally. The damage threshold of single pulse laser for removing oxide on aluminum alloy surface was obtained. The cause and effect of laser damage threshold were researched by combining the results of X-ray energy spectrum. The relationship between the characteristic spectral lines of plasma spectra and the number of pulses in laser cleaning process was researched. Based on the intensity ratio of O/Al characteristic spectral lines, a criterion for on-line detection of cleaning effect and secondary oxidation damage was proposed. To verify the accuracy of the criterion, the trend of the intensity ratio of O/Al characteristic lines with cleaning times was compared with that of oxygen atom percentage obtained by X-ray energy spectra. The experimental results showed that the influence of air atmosphere can be eliminated by analyzing the laser cleaning state with the spectral characteristics of laser-induced plasma in the range of 200～700 nm; The characteristic spectra of oxygen and aluminum elements accurately reflect the composition difference between the oxide film on the surface and the aluminum alloy substrate; The element composition and content detected by X-ray energy spectrum showed that the oxygen content first decreased and then increased with the laser cleaning energy density, and the laser energy threshold of secondary oxidation damage of single cleaning aluminum alloy is 11.46 J·cm-2. The laser energy density less than the damage threshold does not cause damage to the aluminum alloy matrix after multiple cleaning, and the intensity of plasma spectral characteristic lines is correlated with surface states; The ratio of 656.5 nm (O Ⅱ)/396.2 nm (Al Ⅰ) spectral line intensity (≤1.5%) is the criterion of laser cleaning. The research results are beneficial to the real-time control technology of laser cleaning of aluminum alloy and the integration of welding devices.