Abstract: During laser strengthening mould surface, a tiny wave of defocusing amount will generate splash as laser energy reach a certain value, which has strong effect on mould surface strengthening quality. By real-time collecting and processing the picture while laser strengthening the mould surface using CCD coaxial visual, the width of weld bead was extracted as the characteristic quantity of splash under fixed current. Acoustic signal strength has direct relation with laser energy and the relationship between acoustical signal RMS and splash was also investigated. Coaxial visual supplemented by acoustical signal achieve detecting laser strengthening splash using different sensor, improving remarkably the accuracy of splash detecting.