Single bead experiments were conducted to clarify the relationship between process parameters and melt pool geometry based on melt pool characterization, aiming to obtain a better understanding of Electron Beam Melting (EBM) additive manufacturing. INCONEL® 1 718 polycrystalline plate and gas atomization powders were used to generate melt pool geometries by various beam power and scan speed combinations. The surface morphology and cross section microstructures were analyzed. The surface morphology indicates that input energy play an important role in single beads continuity. The microstructure of fully columnar grains is verified by cross-section profile of single beads. Furthermore, the melt pool widths and depth increase almost linearly with beam power on the basis of the cross-sectional geometrical profiles. A reciprocal relationship exists between width/depth ratio and line energy. Finally, process condition has profound effect on crystal growth and grain structure. Grains grow along different direction in relatively high line energy cases. However, grains grow almost along the same direction namely grow vertically in relatively low line energy cases.