Structure determines properties, and properties determine applications, which is an important ideology of natural sciences. For optical materials, it is vital to lucubrate the corresponding relationship between the local crystal structure and luminescence properties for their design, synthesis, and application. This work reports a newly designed Y2Mg2Al2Si2O12:Eu3+ red phosphor, in which difunctional Eu3+ ion is used as a red-light activator and spectroscopic probe. The qualitative and quantitative studies on the relationship between the local crystal structure and the luminescence properties of YMAS:Eu3+ are performed experimentally and computationally, using the Y3Al5O12 (YAG):Eu3+ as contrast. Moreover, compared with YAG:Eu3+ , the newly designed YMAS:Eu3+ has stronger luminescence, superior Commission Internationale de L'Eclairage chromaticity coordinates, a lower optimal doping concentration, and equally excellent thermal stability. The satisfactory color-rendering index of packaged white-light-emitting diodes demonstrates its potential performance as a red phosphor. Briefly, this work provides not only a new case for the study of the local crystal structure and luminescence properties but also a new possibility for the application of a red phosphor in solid-state lighting.