Using the idea of CDMA, an automatic beam selection scheme for indoor diffuse wireless infrared communication systems is p resented. The scheme usesOOC as transceiver identification code, and selects transmitter beam according to receiver correlation value. Communication p rocess includes two phases: beam selection and data transfer. In beam selection, all transmitters aligned to different directions transmit signal at the same time. Recip ient comp letes acquisition and the best beam selection, then initiator is informed of selection result. In date transfer, initiator begins data transfer through the best beam. Simulation results show that compared with ordinary quasi2diffuse link, the p resented method can reduce the average transmitter power by 2.1dB under the condition of the same minimum detectable power. And with the same transmitter power, average irradiance received by detector effective area is increased by 39.67% in our proposed system.