Abstract: Micro Electronics Mechanical Systems involving micro-channels flows have been widely used in microflow control application.Investigation on micro-channel flow characteristics can provide instructions for designing micro mechanical systems.On the basis of gaseous flow scale classification,we discuss the flow characteristics and flow models in different scales.In this paper,we focus on the friction characteristics in fully developed region,inlet and outlet region in both straight and non-straight micro-channel.The micro-scale particle image velocimetry technique and study on flow filed features are summarized.Based on the analysis of present work on micro-channel flow,we conclude that further in-vestigation on friction characteristics in inlet and outlet region,flow characteristics in non-straight micro-channel and un-steady flow characteristics may facilitate the optimization of micro mechanical design and extended application.