Abstract: In order to improve the surface quality of the formed parts of H13 die steel in the process of electron beam selective melting technology and to explore the causes of the defective problems in the forming process, numerical simulations of the thermohydrodynamic behaviors of the melt were carried out based on a randomly distributed metal powder bed model established by the discrete element method. The single-pass results show that the average depth of the single-pass melt pool increases from 15.2 μm to 49.2 μm and the width of the single-pass melt pool increases from 79.2 μm to 140.1 μm when the electron beam power is increased from 600 W to 1080 W and the scanning speed is 1.5 m/s. It is also found that the single-pass shape surface quality is best with an electron beam power of 960 W. The results of the single-pass results are summarized as follows. The two-pass results show that the Z-shaped scanning path leads to roughness at one end of the melt path, and the S-shaped scanning path is prone to heat accumulation in the melt path. When the energy of the electron beam is low, the spheroidization effect and single-path unevenness will occur. When the electron beam energy is high, the heat accumulation in the melt channel is easy to occur, which affects the subsequent shape and size of the melt channel.