Optical antenna for indoor visible light communication has such problems as small field of view, non-uniformity of the irradiance distribution at the receiver, and low received power under the low power light source condition. We design a planar concentrator as an optical antenna and establish a gain theory. We establish a visible light communication system model based on planar concentrators in a 5 m×5 m×3 m room, which use a planar concentrator with a field of view of 50° as an optical antenna. The simulation results show that the received average powers after using the concentrator in the direct link channel and the non-direct link channel are increased by 16.2411 dBm and 16.4956 dBm compared with that under the direct detection.