In this study, we have performed first-principles density functional theory (DFT) calculations to investigate pressure and composition effects on the structural, elastic, and electronic properties of silicon doped RuGe ternary compounds (RuSixGe1-x) for an increasing molar fraction of Si atom from 0.0 to 1.0 by 0.1. For each x composition, we have investigated formation energies of different compositions under three different pressure to study the alloying effects on the stability of RuGe in the B2 structure. It was determined that our calculated lattice parameters were in good agreement with the experimental results and decreased with Si content. The band structures and partial density of states (PDOS) have been investigated as electronic property. Using calculated second-order elastic constants, mechanical properties have been obtained for all x compositions. Among the different compositions for RuSixGe1-x under pressure it has been found that the most stable alloys have been obtained for x = 0.9, 0.7, and 0.6 under 0 GPa, 30 GPa, and 60 GPa, respectively. Elastic and dynamical stabilities were confirmed by Born Stability Criteria and positive phonon dispersion curves. Also, the elastic anisotropy has been visualized in detail by plotting the directional dependence of compressibility, Poisson ratio, Young's, and Shear module.