Abstract: The measuring accuracy of the coal mill inlet air flow rate is very important to the safety, stability and economic operation of the boiler. In this investigation we analyses the characteristics of various coal mill air flow measurement device of the positive pressure direct injection system, and the requirement of air duct before and after the straight section.We research various air duct layout scheme of the flow measurement device and provide the optimized layout scheme.The results shown that we shall select the measurement device with good performance at design time,and ensure the layout design of the straight section length, at the same time need to consider a cold mixed length, and try to create a favorable operating conditions for the air flow measuring device.