In this work the electronic and optical properties of luminescent materials XSiN2 (X = Ca, Sr, Ba) were revisited based on density function theory (DFT) calculations with a newly developed DFT-1/2 scheme. It was found that the DFT-1/2 correction on nitrogen can well correct the band gaps to approach the experimental values, showing its advantage comparing to the Perdew–Burke–Ernzerhof (PBE) and the Strongly Constrained and Appropriately Normed (SCAN) functionals. Then the electronic band structures and optical properties of the three compounds were investigated using the DFT-1/2 scheme. Within the three compounds, the band gap shows a monotonic decrease along with the atomic number of alkali earth metal mainly due to the downshift of the conduction band edge, where the electronic conductivity is primarily based on electron since it shows a much smaller effective mass than hole. CaSiN2 owns more flat valence bands, while SrSiN2 gives lighter electron. Moreover, the three compounds show high optical absorption, but distinct behavior of light absorption and refractivity in specific energy range, suggesting their applications in optical applications.