A series of Y_2.985Al_5-xGa_xO₁₂:0.015Ce (YAGG:Ce, x = 0, 1, 2, 3, 4, 5) transparent ceramics were prepared via a solid-state reaction method. Two-step sintering technique was proved to be an effective approach to prepare functional ceramics with high Ga concentration, and Y₃Ga₅O₁₂ (YGG) transparent ceramic was successfully prepared for the first time. According to the variation of Al/Ga ratio, regulation of band structure and luminescence properties of YAGG:Ce transparent ceramics were effectively investigated. When Ga substitutes Al sites, the tetrahedral site is more favorable compared to the octahedral site for Ga to occupy according to the first-principle calculation. A continuous blue shift of the emission from 565 to 515 nm was achieved as Ga was gradually introduced into Y₃Al₅O₁₂:Ce matrix. High quality green light was obtained by coupling the YAGG:Ce ceramics with commercial blue InGaN chips. Transparent luminescence ceramics accomplished in this work can be quite prospective for high power LED application.