To suppress multiple access interference and multiple noises existing in optical code division multiple access system,a system with hard-limiter and parallel interference canceller based on maximal value decision is presented.The effect of suppress multiple access interference is examined while APD noise and thermal noise exist.Optical orthogonal code is applied as address code,APD is used as opto-electro detector,and bit error rate of the system is derived and analyzed.Simulations based on the expression are done and comparison with other multi-user interference suppressing methods is made.Compared with other effective methods such as single bit with single hard-limiter,single bit with double hard-limiters,multiple-bit transmitted method,multiple-bit transmitted with hard-limiter method,parallel interference canceller(without hard-limiter) based maximal value decision method and so on,simulation results show that the effect of suppress multiple access interference of the system is superior to parallel interference canceller without hard-limier and multiple-bit transmitted method with or without hard-limiter.If the received power is low,the system is also superior to double hard-limiters method.So,it is effective for suppressing multiple access interference and multiple noises.