The modified quadratic congruence codes(MQC) with good relativity is presented in spectral-amplitude-coding optical code division multiple access(SAC-OCDMA) system,the work procedure of encoder and decoder with fiber Bragg gratings(FBGs) are analyzed,the performance of signal noise ratio(SIR) and the bit error rate(BER) are also analyzed under the conditions that the light source is approach Gaussian profile over the whole bandwidth and the multiple access interference(MAI) is considered.The results show that SIR of the MQC constructed with primes p=5 and p=7 increases by 13 db and 20 db as compared with that of the M sequences under the condition of same simultaneous users.The capacity of MQC system is much larger than that of the M sequences system with almost the same code length and the same BER.It indicates that the SAC-OCDMA with MQC is priority to other scheme available.