Pure tungsten specimens were prepared by additive manufacturing of selective electron beam melting(SEBM). The heat transfer process during SEBM and microstructure characteristics of pure tungsten were analyzed. The results show that the microstructure is columnar crystal grown in the form of epitaxial growth. In the inner side of the sample, the heat conduction along the building direction of the sample is dominant. The columnar crystal growth direction is opposite to the heat flow direction, forming a cylindrical crystal with complete vertical growth; In the outer side of the sample, the heat conduction are the joint action of conduction along the building direction and conduction to the powder bed. This makes the direction of the heat conduction deviate from the building direction, so the columnar crystal is 30-45_⁰ angle with the building direction. Furthermore, the preferred orientation of [111] and [100] is formed along the building direction in the SEBM pure tungsten.