The optical properties of cubic TiBN is important for understanding optical properties of TiBN films, monitoring and controlling the growth of TiBN films. Optical properties of cubic TiBN were investigated by using plane-wave ultrasoft pseudopotential method based on density functional theory. Electronic states density, dielectric function, absorption coefficient, reflectance, refractive index, and extinction coefficient of cubic TiBN were calculated and analysed. density of states results demonstrates that there are peaks that attributed to the 2p states of B, which is considered to have a substantial effect on the optical absorption properties of cubic TiBN. Meanwhile, the colorimetric coordinates of cubic TiBN were calculated, based on which the corelations between colorimetric coordinates of TiBN films and technological parameters were analysed.