Microstructure characteristics of the laser melting deposited TC17 titanium alloy components were analyzed by OM, SEM and XRD. The solid-state phase transformation and the microstructure evolution under the effect of laser short term cycle of heating and cooling were researched. Results show that the laser melting deposited TC17 titanium alloy consists of directionally solidified “knuckle” grains and a few equiaxed grains, which are arranged alternately. The microstructure of the laser melting deposited TC17 titanium alloy is fine duplex microstructure composed of irregular primary lamellar a and basketwave transformed β. Solid-phase transformation is shown in the last twelve depositing layers: the microstructure in the last four layers is Martensite; in the 5th to 7th layer is mainly acicular a and a little irregular coarse a; in the 8th to 12th layer is coarser and shorter a with underdeveloped serrated interface and the second a is fine basketwave microstructure.