Laser melting deposition (LMD) combines the laser cladding and rapid prototyping manufacturing technologies, and can be used for swift prototyping of complex parts with excellent comprehensive properties. However, due to its unique metallurgical conditions, it is easy to develop penetrating columnar crystals and coarse primary grains along the building direction. This remarkably reduces the mechanical properties of the alloy. The root cause of this issue can be traced back to the thermodynamic and dynamic metallurgical processes. Thus, this study proposes an oscillating laser melting deposition (OLMD) based on laser oscillating welding technology, and aims to elucidate the metallurgical structure and defects of laser melt deposition. OLMD modifies the motion trajectory of the molten pool using a laser in situ oscillation, and directly impacts the temperature gradient and solidification rate, thus improving the microstructure of titanium alloy by LMD. Furthermore, the microstructure evolution and mechanical properties of TC4 titanium alloy produced using OLMD were studied using OM, SEM, EBSD, and a Vickers hardness tester. The results indicate that the optimum process parameters of laser melting deposition without oscillation are as follows: the laser power is 1000 W, scanning rate is 8 mm/s, and powder feeding rate is 6.92 g/min. The optimum technological parameters of linear oscillation are as follows: the frequency is 200 Hz and the oscillation amplitude is 1.5 mm. Addition of linear laser oscillation considerably improved the morphology of the molten pool, and defects such as porosity and cracks were not observed. The overall number and size of columnar crystals reduced, and the grains were equiaxed. When compared to the sample without oscillation, the average grain size of Ti-6Al-4V alloy with linear oscillation decreased from 5.20 μm to 4.37 μm, while hardness increased from 418.00 HV to 428.75 HV.