Electron beam melting (EBM) is one of the powder-bed fusion additive manufacturing technologies. This technology is very suitable for producing near-net-shape small to medium volume metallic parts with complex geometries. However, layer-by-layer fusion step introduces rapid thermal cycles, which results in a different microstructure as compared to their cast or wrought counterparts. Therefore, the microstructure and mechanical properties produced by EBM must be better understood and in turn to control the microstructure for requirements of some specific applications. Accordingly, in this paper, an insight will be provided on the effort of understanding the microstructure and mechanical properties from atomic scale to real complex big-sized industrial components. The spatial- and geometrical-based microstructure and mechanical properties of EBM Ti-6Al-4V as well as the effect of heat treatment on them were investigated using atom probe tomography, transmission electron microscopy, scanning electron microscopy, optical microscopy, x-ray diffraction, x-ray computed tomography, nanohardness testing, microhardness testing, tensile testing and finite element simulations. The microstructure and deformation mode depend on both the build thickness and build height which are closely linked to the heat input and the cooling rate in EBM process. Furthermore, the control of microstructure by varying the process parameters and heat treatment schemes was also proposed. By using these findings, an impeller prototype with a base diameter of 100 mm, a height of 53 mm and thinnest sections of ~0.7 mm and a turbine blade prototype with dimensions of 180×70×360 mm were successfully fabricated by EBM. These components exhibited an overall improved combination of strength and ductility as compared to the counterparts fabricated by conventional methods. These results revealed that EBM is a promising method for fabricating complex-shaped industrial components with superior mechanical performance for practical application.