<p>The exploration of Ru-B compounds is motivated by their potential to exhibit superior hardness and thermal stability for advanced material applications. However, current research mainly focuses on a few known phases, and a systematic exploration of more Ru-B phases is needed. The structures, mechanical, and electronic properties of ruthenium-boride compounds were systematically investigated by the structure prediction algorithm combined with first-principles calculations. Our results indicate that RuB (<i>P</i>-6<i>m</i>2), Ru₂B₃ (<i>P</i>6₃/<i>mmc</i>), and RuB₂ (<i>Pmmn</i>) are thermodynamically stable phases at zero pressure, while Ru₂B₅ (<i>R</i>3<i>m</i>) and RuB₃ (<i>P</i>-6<i>m</i>2) are kinetically stable metastable phases. Analysis of the mechanical properties reveals that the Vickers hardness increases with boron content in these compounds, and the RuB₃ (<i>P</i>-6<i>m</i>2) shows the highest value of 19.8 GPa. Further analysis shows that RuB₂ (<i>Pmmn</i>) and RuB₃ (<i>P</i>-6<i>m</i>2) are the most pronounced and weakest elastic anisotropies among the five compounds, respectively. However, RuB₃ (<i>P</i>-6<i>m</i>2) possesses the highest Debye temperature and the relatively low thermal conductivity, suggesting its application potential in thermal barrier coatings. Finally, an inspection of the electronic structure and chemical bonding evidence that all compounds display metallic behavior, characterized by strong hybridization between Ru-<i>d</i> and B-<i>p</i> states, and B-B covalent bonding strengthens with increasing boron content. These findings provide a theoretical foundation for understanding the bonding nature, stability, and mechanical behavior of the Ru-B system and offer valuable insights for the future experimental synthesis and application of boron-rich transition metal borides.</p>