Abstract: The gas-liquid two-phase intermittent flow pattern and pressure drop characteristics in parallel microchannels with expansion-constriction cross sections were investigated experimentally by means of the IDT high-speed camera mounted together with a Nikon microscope.The results showed that,with the change of the gas-liquid two-phase superficial velocity,the annular/liquid alternating flow pattern,the slug/annular/liquid alternating flow pattern,the slug/liquid alternating flow pattern,mist/slug/liquid alternating flow pattern and mist/liquid alternating flow pattern presented in turn.The two-phase flow regime maps for the parallel microchannels with expansion-constriction cross sections were obtained.The homogeneous flow model cannot predict the two-phase pressure drop data.Despite the separated flow model introducing the gas-liquid two-phase interaction to a certain extent,the gas-liquid two-phase movement and space distribution in the parallel microchannels with periodic expansion-constriction cross sections cannot be predicted accurately.