To content large part manufacturing of the airplane, electron beam welding (EBW) was employed on TC4 titanium alloy with 170 mm thickness, which was investigated by the method of induced molten pool flow. The experiments with variable focusing welding were conducted on the plates, which achieved the underfocusing processing under the current of 2415–2400 mA. The maximum of welding depth reaches 162 mm, and weld morphology is parallel, which contributing to the fluidity of molten pool and welding formation. The microstructures in weld area are coarse crystals and acicular martensite α', which became gradually refining and homogeneity with the welding penetration increasing. The microhardness of the joint presents the saddle-shaped distribution along the cross section, which gradually increases from 337HV to 356HV along welding depth direction. The investigation verified effectiveness of the EBW processing with induced molten pool flow, which can improve the penetration forming, weld morphology, and microstructure uniformity of large-thickness titanium alloys.