Abstract: The authors analyzed the marsh gas and gas components, thermal chemical differences and combined with fluid damics, combustion principles and other knowledge.The spool section, lift, air pressure, flow characteristics of the mutual relations are deeply researched.The the corresponding model for flow characteristics and the engine test validation are established.The result indicates that the increase in power is 17% for engine 4100 compared with the original natural gas fuel supply devices.It verifies the correctness of the proposed method for supply spool design.