Driven by the emergence of cloud computing and high- bandwidth applications, the efforts of next generation passive optical network (NG-PON2) should be made on ultra-high capacity, long location and wide coverage. With the development of NG-PON2 technology, the structure of passive optical network (PON) system is also becoming more and more complex and heterogeneous. The traffic imbalance problem begins to appear in optical line terminal (OLT) of PON which is caused by the imbalanced utilization of link and port resources in conventional core networks. The downstream traffic balancing problem base on OLT of 40 G coherent PON system is proposed and discussed. In addition, a novel dynamic traffic balance strategy for the higher blocking probability and lower bandwidth utilization problems of 40 G coherent PON system is discussed. The experimental results show that the proposed dynamic traffic balance strategy can efficiently reduce the blocking probability and improve the bandwidth utilization.