Abstract: To solve the problem of grain coarseness in pure tungsten prepared by selective electron beam melting (SEBM), B was selected as the grain refinement element. The influence of forming process parameters on the densification, microstructure, and mechanical properties of the W‒B alloys was investigated. It is found that when the electron beam current intensity is 15 mA, the scanning speed is 300 mm·s^‒1, and the volume energy density is 1200 J·mm^‒3, the density of W‒B alloy samples is the highest, the pores and unfused powders are the least, and the microcracks are basically suppressed. The constitutional undercooling caused by element B effectively refines the grain size of W formed by SEBM, and the microstructure changes from coarse columnar crystal to fine columnar dendrites with an average size of ~8.26 μm. The highest hardness of the W‒B alloys is HV 672, and the highest ultimate compressive strength is 1598 MPa. The fracture mechanism is mainly cleavage fracture.