Optical code division multiple access (OCDMA) passive optical network (PON) can find wide applications in the next optical access network. One of its key techniques of is construction of address code. Aiming at the facts that (F,K,1) optical orthogonal code (OOC) possesses good performance but capacity is small, and number of users in OCDMA PON is not very big thereafter OOC auto-correlation or cross-correlation may not be very strict, (F,K,2) OOC can be used as address codes for OCDMA PON. In this paper, the method of constructing OOC based on block design is discussed. The algorithm of construction (F,K,2) of OOC from block design is presented and simulated; several groups of (F,K,2) OOC are gained. The results show that the algorithm has good astringency and simplicity. It can construct (F,K,2) OOC effectively. It is feasible.