In-situ, real-time online monitoring technology helps improve the controllability of the aircraft skin removal process. Laser Induced Breakdown Spectroscopy (LIBS) is a highly efficient and fast elemental analysis technique, which realizes intelligent laser-controlled paint removal by quickly analyzing the elemental changes in the paint layer through the plasma spectral information generated during the laser's interaction with the material. LIBS technology has also demonstrated various potential applications in geologic exploration, compositional detection, process monitoring, etc. However, due to the limitation of the outer contour or surface morphology of the monitoring object, it is inevitable to use LIBS technology for exploration, detection, and monitoring. However, due to the limitations of the monitoring object's outer contour or surface morphology, when LIBS technology is used for detection, testing and monitoring, it is inevitable that the laser will act on the material surface in a non-perpendicular incidence mode, which will lead to fluctuations in the intensity and stability of the induced plasma spectra and affect the results of the geological detection, compositional testing and process monitoring based on LIBS technology. Therefore, in order to improve the accuracy of LIBS analysis, it is necessary to consider the effect of laser incidence angle on the intensity and repeatability of LIBS spectra. For the online monitoring of laser paint removal LIBS on free-form surfaces or geometrically mutated regions of aircraft skin, the paper collected LIBS spectra under different laser incidence angles, used baseline correction to preprocess the data of the original spectra, and selected six characteristic spectral lines as the analysis spectra, and studied the changing rules and causes of the laser incidence angle on the intensity of the characteristic signals of the LIBS spectra and their repeatability. The results show that in the range of laser incidence angle from 90° to 60° (5° interval), the intensity of the characteristic peaks decreases with the decrease of the laser incidence angle in a general pattern of “increasing first and then decreasing”, in which the characteristic spectral line Ti Ⅰ 429.926 nm has a better sensitivity and response to the laser incidence angle. When the laser incidence angle is 75°, the characteristic peak intensity of the characteristic spectral line Ti Ⅰ 429.926 nm increases by nearly 145% compared with that of the laser incidence angle of 90°，which indicates that the selection of the laser incidence angle is conducive to the enhancement of the spectral signal quality and signal intensity. In addition, the characteristic peak intensity of the characteristic spectral line Ti Ⅰ 429.926 nm has a better repeatability in the range of 75°～65° laser incidence angle, while the characteristic peak intensities of the rest of the elements have a better repeatability at the laser incidence angle of 85°. This study illustrates the connection and difference of the LIBS feature spectra when the laser is incident in vertical and non-vertical ways, and reveals the mechanism of the laser incidence angle on the multi-dimensional characteristics of the LIBS feature signals, which can be used as a reference for the detection, testing, and monitoring of LIBS when the laser is not incident vertically.