The maximum fiber distance of Ethernet Passive Optical Network(EPON) is specified to be no more than 20 km in IEEE802.3-2008.But in some practical applications,the fiber distance needs to be up to scores of kilometers.The methods of extending the transmission distance of EPON system are discussed in this paper,and it is found that by partly changing the EPON physical layer and Multi-Point Media access Control(MPMC) sub-layer,the required transmission distance can be achieved.