The mechanical and thermodynamics properties of Mo5Si3 and Mo5SiB2 have been investigated by using the first-principle calculations. The cell structure parameters with pressure are briefly discussed. The values of micro-hardness and melting point of both Mo5SiB2 and Mo5Si3 are studied. In addition, both composite alloys' elastic constants Cij and elastic modulus (B, G, E) are close to increase linearly with pressure. The B/G ratios and Cauchy pressure (C12-C44) were also investigated by this method, and the results suggest that pressure can improve the ductilityIP: proper8.46.247.10ties ofOn:both Mon, alloys.07 NovThe 2022 Poisson's09:2 :55ratio indicates that the two alloys are bonded mainly metallic. Finally, the Debye tmperaturwth presure concluded from elastic constants Copyrght: American Scientific Publishers was studied, and the temperature dependence of thermodynamic properties, including the entropy, constant Deivered by Ingenta volume heat capacity (CV ), enthalpy, and Gibbs free energy, are also studied and discussed.