To design solid solution is an effective strategy for functional materials. The complex electron correlation and non-equilibrium atomic interaction are the primary factors to impact the macro-/micro-structure and application performances of solid solution. Hence, this article concentrates on the stable crystal structure and the corresponding electronic structure of Ru1-xTixO2 solid solution by using density functional theory calculations. Based on analyzing the atomic interaction between solute and solvent atoms, the most stable supercell models for the specific solid solubility were obtained. In Ru1-xTixO2 solid solution, solute (and solvent) atoms preferentially arrange along the [110] direction, and tend to occupy the nearest sites of identical atoms, to arrange the symmetric ordered substitution configurations. Using the subregular solution model, the mixing enthalpy can be represented by the following expression: Delta Hf=XTiO2XRuO235.30XTiO2+23.08XRuO2. The calculated phase diagram is consistent with the experimental results. Thus, the calculated results in this article are reliable and can provide more meaningful information. In the cases of Ru-rich solid solutions, the metastable phase exists in the range of x < 0.27; while in the cases of Ti-rich solid solutions, the metastable phase exists in the range of x > 0.81. Interestingly, the electron density of Ru1-xTixO2 solid solutions at Fermi level has a stronger dependence on the Ru composition, which intrinsically influences its electronic structure and optical properties. According to the basic application principle, Ru1-xTixO2 solid solutions with lower (x < 0.27) and higher (x > 0.81) solid solubility could act as suitable candidate for the applications in field electrochemistry and photocatalysis.