The titanium alloy powder preheating process in electron beam melting (EBM) was investigated, and the connection mode among powder particles after preheating was analyzed. The results show that when the Ti6Al4V powder is preheated to above 600 °C during EBM process, a powder aggregation is formed. The sintering mechanism is that small particles partially or completely melt and play the role of binder to bond the majority of big particles together; this will be not only to help the particles to hold their places, withstanding the impact force of electron beam, but also to prevent the spheroidization effect in the prototyped surface. Using Ti6Al4V powder as starting material and adopting complete preheating of the powder layer, the column samples with full interlayer bonding and excellent mechanical properties are produced.