In term of the problem of multi-user interference existing in optical code division multiple access (OCDMA) system, a parallel interference suppressing method for OCDMA communication based on maximal value decision is examined, and the situation is that APD is adopted and multiple noises exist. The fundamental is stated, that is it avoids the case no optical pulse existing while bit 0 is transmitted by adopting a spread spectrum code and its shift as the address codes of bit 0 and bit 1, respectively; and maximal value decision instead of threshold decision is adopted as decision circuit. Optical orthogonal codes is applied as address codes, APD is used as opto-electro detector, and bit error probability of novel system is derived and analyzed. Simulations based on the expression are done and comparison with other multi-user interference suppressing methods is made. The results show that the effect of the method to suppress multiple access interference is changed with different number of system users and code weights; compared with other effective methods such as double hard-limiters method or multiple-bit transmitted method, the method is superior to multiple-bit transmitted method, it is also superior to double hard-limiters method in the case received power is low. So, the method can suppress multi-user interference effectively.