In this paper, we conducted a comprehensive and in-depth theoretical study on the geometric structures as well as electronic and optical properties of B-N analogues of C18, (BN)nC(18-2n) (n = 1-9). All molecules are strictly planar, and their average lengths as an example, the anisotropy of the (hyper)polarizability components was visually demonstrated using the unit sphere representation of (hyper)polarizability, the spatial contributions of important diagonal tensorial components were graphically analyzed using (hyper)polarizability density analysis, and the structural origins of (hyper)polarizability were discussed using (hyper)polarizability decomposition. The frequency dispersion effect of the applied electric fields was observed to have a positive impact on the (hyper)polarizabilities of the molecules studied.