The work aims to enhance the surface hardness and wear resistance of Ti-6Al-4V alloy and solve the failure problem. Laser nitriding treatment was conducted toTi-6Al-4V alloy in pure nitrogen atmosphere by diode laser and the effect of different heat inputs on the quality of nitriding layer under the coupling of laser power and scanning speed was studied. The phase composition, cross-sectional micro-structure and element distribution of nitriding layer were characterized by X-ray diffraction (XRD), scanning electronic microscopy (SEM) and energy dispersive spectrometer (EDS), respectively. The hardness distribution of nitriding layer was measured by microVickers hardness tester. TiN phase was formed in nitriding area of Ti-6Al-4V titanium alloy under different heat inputs, and the volume fraction of TiN phase increased with the increasing heat input. Meanwhile, the thickness of the nitriding layer increased approximately linearly with the increasing heat input. The nitriding layer consisted of continuous TiN layer, columnar crystals, needle crystals and dendrites in turn from surface to inside, and the hardness decreased with the increase of nitriding layer thickness. With the increase of heat input, the number of coarse dendrites and the thickness of nitriding layer increased. However, when the heat input was up to 320 J/mm, the cracks were found in the nitriding layer. A crack-free nitrided layer with a good surface and thickness of about 413~517 μm can be prepared on the Ti-6Al-4V alloy surface by laser gas nitrided technology through regulating the heat input to 210~275 J/mm, and the near surface hardness is over 2.5 times than that of the substrate.