Variable-weight optical orthogonal codes(VW-OOC) are put forward to provide differentiated quality of service(QoS) for different users.Due to its non-fixed code weight,the VW-OOC is larger in capacity than constant OOC.In this paper,the definition and the bound on capacity of VW-OOC are given.The method of designing VW-OOC is presented,and the structure results of the proposed codes are given.In the end,the bit error rate(BER) of multi-user interference for different number of code weight is compared through emulation and theoretical analysis.Results show that the BER of larger code weight is smaller while the number of code weight is the same,and the BER of larger number of code weight is smaller while the code weight is the same.