Velocity distribution among microchannel plays an important role in the performances of microchannel reactors. The optimization of structural parameters by enabling narrow uniform velocity distribution among microchannels is regarded as one of the effective design methods. On the basis of the previously developed model, the effects of structural parameters on the velocity distribution are studied and the relationship between frictional resistances and pressure drop are investigated in this work. It is found that the variation of pressure drop distribution among microchannels due to the variation of frictional resistances is the underlying reason for the variation of velocity distribution among microchannels. Compared with the manifold structural parameters, the microchannel structural parameters show more influence on the velocity distribution. High-aspect-ratio microchannels are in favor of obtaining relatively uniform velocity distribution. By the combination of the calculation of frictional resistances with descriptive geometry, it can predict the trend of velocity distribution among microchannels with the variation of structural parameters without applying complicated theoretical model or numerical simulation. (C) 2010 Elsevier B.V. All rights reserved.