(Mg_1-x-yBa_xSr_y)_1.95SiO₄∶0.05Eu phosphor series samples were prepared by high-temperature solid-state method (at 1 150, 1 200 and 1 250 ℃). By XRD, PL and photograph records under UV lights, the composition- phase-emission light color relationship was established, and the ternary color diagram was then derived. The influence of fabricated temperatures, both on phase constitution and on emission color, was investigated too. Phase analysis showed that (Mg_1-x-yBa_xSr_y)_1.95SiO₄∶0.05Eu powder would gradually change in phase constitution. Starting from Ba₂SiO₄ corner, the powder is a single phase till to the ones with the composition having maximum Mg²⁺ or Sr²⁺ solution. For Sr₂SiO₄ or Mg₂SiO₄ corner, there are two phases in the powder. Phase constitution is gradually complicated as Mg²⁺, Sr²⁺, Ba²⁺ contents are almost the same to each other. Furthermore, the higher the fabricated temperature, the larger Ba₂SiO₄-single-phase region is. At 1 150, 1 200, and 1 250 ℃ the solid solubility of Mg²⁺(Sr²⁺) were 20_at% (30_at%), 30_at% (35_at%) and 35_at% (40_at%). For the mixed-phase region, the number of phase components for the same composition is reduced. PL spectral analysis shows that the green emission is strong and red emission is weaker for the same sample under the excitation comparing 365 nm with 254 nm. The emission color and intensity under ultraviolet excitation change also gradually. Ba₂SiO₄-phase powders are green phosphors, and its emission intensity increases as the Sr²⁺ and Mg²⁺ solution. For the mixture region, the powder changes from green to red phosphor as Ba²⁺ content decreases, and red phosphors’ brightness decreases gradually as Mg²⁺ content decreases. For example, (Mg_1-ySr_y)_1.95SiO₄∶0.05Eu series changes from bright red to dark red phosphor as y increases. When the fabrication temperature is increased, the overall brightness of the phosphor in the Ba₂SiO₄ single-phase region is improved with the Mg²⁺, Sr²⁺ content increases in brightest phosphor composition. The increasing of fabrication temperature also makes the emission intensity of the phosphors in mixed phase region increase, and the green phosphor region becomes larger (under 254 nm excitation, the red-green transition point of (Mg_1-xBa_x)_1.95SiO₄∶0.05Eu is x_{1 150 ℃}=0.5, x_{1 200 ℃}=0.4, x_{1 250℃}=0.3, (Ba_1-ySr_y)_1.95SiO₄∶0.05Eu is y_{1 150 ℃}=0.6, y_{1 200 ℃}=0.7, y_{1 250 ℃}=0.8, (Ba_x(Mg_0.2Sr_0.8)_1-x)_1.95SiO₄∶0.05Eu is x_{1 150 ℃}=0.5, x_{1 200 ℃}=0.4, x_{1 250 ℃}=0.3. The work has a systematic search on the relationship among composition-structure (phase constitution)-fabrication (temperature)-property(luminescence) for (Mg_1-x-yBa_xSr_y)_1.95SiO₄∶0.05Eu powder, and screened out a series of good phosphors, for examples as (Mg_0.35Ba_0.6Sr_0.05)_1.95SiO₄∶0.05Eu/(Mg_0.6Sr_0.4)_1.95SiO₄∶0.05Eu. Single-phase green phosphor is brighter than mixed-phase green phosphor. The solubility increasing can improve Ba₂SiO₄ single-phase green phosphor intensity. The higher fabricated temperature, the larger single-phase green phosphor region, the larger mixed-phase green phosphor region, and higher luminescent intensity for (Mg_1-x-yBa_xSr_y)_1.95SiO₄∶0.05Eu phosphors. (Mg_1-x-yBa_xSr_y)_1.95SiO₄∶0.05Eu emission light color dependence of the composition and temperature would be applied to other phosphor series, and it can also give a guide for new luminescent material discovering.