Phosphor is an important part of the new generation of light-emitting diodes (LEDs), which requires high luminous intensity and high-temperature resistance. In this study, a series of excellent (Ba_1−x−yCa_x)AlSi₅O₂N₇:yEu²⁺ phosphors was developed, which were synthesized by a high-temperature solid-state reaction in a reducing atmosphere. In addition, the crystallinity and luminescence intensity of the samples could be enhanced by some amount of Ca²⁺ substitution. The luminescence intensity was the highest when the Eu²⁺ concentration reached 0.06. Furthermore, the thermal stability of the luminescence was studied in detail. The results were satisfactory, showing that the luminescence intensity of the (Ba_1−xCa_x)AlSi₅O₂N₇:Eu²⁺ phosphors exhibited unique negative-thermal-quenching characteristics both at high (273–473 K) and low (4–273 K) temperatures. And the phosphor combined with UV LED chip and red phosphor Sr₂Si₅N₈:Eu²⁺ can achieve a CRI of 90.4 in white LED application which indicated the (Ba_1−xCa_x)AlSi₅O₂N₇:Eu²⁺ phosphor has potential in LED applications.