Study on the mechanism of laser polishing of titanium alloy Ti6Al4V is of great significance to improve the surface quality and performance. A nanosecond pulsed fiber laser was used to polish an 8 mm×8 mm local area of the titanium alloy with a bow-shaped scanning path. Polarized light microscope and optical surface profilometer were used to observe the two-dimensional and three-dimensional morphology of polished material surface and measure the surface roughness. The effect of different laser power, overlap rate, pulse width, scanning times, and surface roughness on the surface roughness of titanium alloy was studied. The properties of the polished materials were analyzed by automatic microhardness tester, scanning electron microscope and X-ray diffraction analyzer. The results show that with the increase of the average laser power, the spot overlap rate and the scanning times, the surface roughness of the titanium alloy decreases first and then increases. With the increase of pulse width, the surface roughness of titanium alloy shows a downward trend. The greater the original surface roughness is, the greater the reduction rate of the surface roughness polished will be. The smaller the original surface roughness is, the smaller the surface roughness polished will be. The minimum surface roughness of titanium alloy is 0.164 μm, and the roughness reduction rate is 60%. The microhardness of the polished material was increased 6% compared with the matrix. After polishing, the surface structure of the titanium alloy changes from white equiaxed α-Ti6Al4V to fine needle-like martensite α′-Ti6Al4V.