In order to realize the densification behavior of pure tungsten processed by selective laser melting, the single layer laser melting and solidifying of pure tungsten substrate and powder experiments are conducted to find the optimal processing parameters, and the balling phenomenon is observed. The balling process is explained with spreading and solidifying of the molten droplets competition model. The pure tungsten droplets spread at a low speed for their high viscosity and surface tension, but they solidify simultaneously at a high speed driven by the existing steep temperature gradient. Due to their higher thermal conductivity and melting point, the molten droplets solidify entirely before spreading completely and keep their globular geometry instead of creating a flat layer. Increasing the laser absorptivity of powder and substrate helps reduce the balling tendency at the higher peak temperature. Compared with scan speed, adjusting the laser exposure time is more appropriate under pulse laser control. Favorable melt tracks can be fabricated with exposure time of 300 μs, for the balanced melt volume and temperature gradient.