First principal computations have been made to explore the optical and electronic characteristics of Cs2AgBiX6 (X=Cl, Br, I) double perovskite. To determine the band gap energy we have used the GGA potentials. The values found for I, Cl, and Br are 0.815, 1.417, and 1.836 eV, respectively. According to our numerical simulation, the Cs2AgBiX6 (X=Cl, Br, I) has an important light absorption coefficient, exceeding a value of 104 cm-1 which makes it a viable absorbing material for solar systems. Other optical properties such as refractive index and dielectric function were also computed in this work. We have found = 7.72, = 5.22, and = 4.12 for I, Cl, and Br, respectively. Regarding the equivalent static refractive indices values of Cs2AgBiX6 (X=Cl, Br, I), we have found 0= 2.77, 0= 2.28, and 0= 2.03 for I, Br, and Cl, respectively. Also, we have used SCAPS software to simulate solar cells made of Cs2AgBiX6 (X=Cl, Br, I). The efficiency, fill factor, and other parameters have computed. Our results are 1.52, 1.08, and 0.54 V and 16.56, 28.65, and 50.25 mA∕cm2 in Voc and Jsc for Cl,Br and I, respectively.