A differential equation of motion for gas-flour two phase Tow in a vertical pipe was first derived based on the momentum conservation and by adopting two empirical expressions for the velocity ratio of flour to gas and frictional coefficient between four and pipe wall, and then a pressure drop model for dilute positive pneumatic conveying of four through a vertical pipeline was developed by employing the continuity and state equations for gas. The conveying tests were conducted on a positive pneumatic conveying system of four in a flour mill. Under each of the sit different flow conditions, the conveying parameters, such as the four and gas mass Tow rates and the pressure drop between two selected cross sections on the vertical pipeline were measured. The pressure drop between the two selected cross sections was evaluated using the pressure drop model for each of the six flow, conditions. The calculated values of pressure drop agree well with the measured data, and it is demonstrated that the model is applicable to vertical positive pneumatic conveying systems of flour.