Eu2+ doped strontium aluminate phosphors CaySr4−x−yAl2O7:xEu2+ (0 ≤ x ≤ 0.1, 0 ≤ y ≤ 0.1) were synthesized via a novel halide-assisted solid-state reaction method. The phase structure and photoluminescence properties of CaySr4−x−yAl2O7:xEu2+ were characterized via X-ray diffraction (XRD) and fluorescence spectrophotometer. The XRD patterns indicate that the α-Sr4Al2O7 phase structure with negligible impurities were produced in the samples of CaySr4−x−yAl2O7:xEu2+ (x ≤ 0.1 and y ≤ 0.1) at 1450 °C. Photoluminescence results show that the CaySr4−x−yAl2O7:xEu phosphor with NH4I as reductant presents typical intense Eu2+ red emission bands centered at 610 nm while excited by 450 nm. Accordingly, samples without NH4I only exhibit two weak Eu3+ emission peaks located at 598 and 619 nm, respectively. It can be ascribed to the reduction characteristic of I− ion. Furthermore, by partial replacement of Sr2+ with Ca2+ in Sr4Al2O7 host, the emission intensity is enhanced up to 260% with emission peak red shifted by 5–10 nm. These results indicate that partial substitution of Sr2+ by Ca2+ is an efficient way to increase the proportion of longer wavelength emission and luminescence intensity for Sr4Al2O7:Eu phosphors.