Abstract: In order to reveal the relationship between blue-violet light signal and the surface quality in cladding process,the blue-violet light signal intensity was measured in real time with a UV-420 device.The blue-violet intensity was obtained at different scanning speeds and laser power.Experimental and analytical results show that the surface quality is good when blue-violet intensity is relatively stabled at 1.7μW/cm2～2.5μW/cm.And the plasma is mainly caused by the breakdown of powder's vaporization.The blue-violet intensity can reflect the surface quality,and it can also provide parameters for closed-loop feedback control.