In order to improve the performance of optical wireless communication system,a novel fixed length dual-amplitude pulse interval modulation-code division multipte access (FDAPIM-CDMA) is proposed. With the optical orthogonal codes (OOC),the bit error rate (BER) of the proposed system in chip synchronous interference and ideal chip asynchronous interference are analyzed respectively. The upper and lower bounds on BER are derived as a function of code length,code weight,number of users,and receiver threshold. The characteristics for a variety of system parameters are discussed and compared with on-off keying-code division multiple access (OOK-CDMA). Simulations show that the BER performance of the proposed system can be improved by longer code length and smaller number of users. It is effective to get the threshold level higher to improve the system performance when the code weight is larger. Moreover,both the upper and lower bounds on BER of FDAPIM-CDMA are lower than those of OOK-CDMA when the bits per symbol are not less than 6. Hence,FDAPIM-CDMA plays good performance in multi-user interference and is superior in wireless optical communications system.