We use first-principles calculation with pseudo-potential and plane wave method to study the bulk meduli, electronic structures and optical properties of copper halides CuX (X = Cl, Br, I). A comparison of the calculation results with the available experimental results show that it is more suitable using the generalized gradient approximation to study these properties than using the local density approximation. The results show that valence bands of CuXX(X = Cl, Br, I) are dominated by the d bands of Cu. Conduction bands are mainly from s bands of Cu and halide atoms, as well as from p bands of halide atoms. The calculated refractive indices of CuX(X = Cl, Br, I) are 1.887, 2.015, and 2.199, respectively. These results are in good agreement with the those calculated from the Gladstone-Dale relationship.