In this study, the nitrided layer was prepared on Ti6Al4V alloy by laser gas nitriding using the scanning galvanometer (G-LGN). Its typical features were investigated in comparison to that using the diode laser with robot (D-LGN) under the same energy density and treated area. In order to reveal the connections between the cavitation resistance (CE) and characteristics of the nitrided layer, the samples were characterized by OM, SEM, XRD, XPS, laser scanning microscopy, and microhardness tester. Due to using the scanner, the G-LGN method is given a smaller laser spot size (micrometer scale), higher scanning speed, and remelting brought by successive overlapping during processing. Those cause it different from the D-LGN method in the microstructure and CE resistance of the nitrided layer. The results show that the G-LGN sample has a more uniform surface with a lower average surface roughness (Sa = 3.043 μm) compared with the D-LGN sample. Moreover, the TiN dendrites with smaller sizes and an amount of TiN0.3 phase are formed in its nitrided layer. It is interesting that the TiN0.3 phases in the G-LGN sample result in a lower surface hardness (about 700–800 HV) with respect to the D-LGN sample, but a more uniform hardness distribution through the depth direction can be detected. According to the results of the CE test, the G-LGN sample exhibits the lowest cumulative mass loss and mean erosion rate during the whole erosion time in comparison to the substrate and D-LGN sample, suggesting the best CE resistance. Therefore, the G-LGN method will provide competitive advantages over the D-LGN method for the CE protection of the titanium components owing to the improvement in the quality and performance of the nitrided layer as well as the superiority of the scanning galvanometer.