With designing air pads on silicon-on-insulator (SOI) wafer periodically as a cellular structure, a 1×2 photonic band gap (PBG) beam splitter is proposed in this article. We study the characteristics of the designed 1×2 SOI PBG beam splitter and simulate the relationship of the two output power with the launching wavelengths. We use finite-difference-time-domain (FDTD) as simulation technique. The propagation of the light and the spectral response are simulated. The device we designed has the total length 4.46 μm and the total width 7 μm.