Forecast of freight traffic is not only a key problem in the process of design transport development programming，but also a main support to decision of transport company．The method regression that usually used is an average trend of varable itself，this method cannot show the efficiency between input and output．If we want know efficient output of transport system and find out approach to improve efficiency of input，we should fmd another method．A foreesst model of DFA is set up in this paper that based on the Input-Output theory to investigate this problem．Example show the method is efficient in practices．