Optical code-division multiple-access system, usually known as OCDMA, can provide very attractive features, such as asynchronous access, privacy and security in transmission, ability to support variable bit rate and scalability of the network. A time/frequency encoding/decoding OCDMA system with high quality Bragg grating arrays is developed, and transmission rates up to 1.4 Gb/s per user can be achieved. The effects of data rate on the performance of the system are studied theoretically and experimentally. It is proved that even if the data rate is beyond the critical value determined by the distance between Bragg gratings essential for the prevention of code overlapping, the performance of the system can still be satisfying，when the user number is lower than (3/2) times of Ps (pulse number of time in a code) or the code length is larger than 289, the system's error rate will not increase obviously as the data rate exceeds the critical value.