Practically investigate water removal and cell performance for PEMFCs under low gravity circumstance is an urgent task, especially as a promising power supply unit applied to space engineering. PEMFC with an in-situ optical flow field was used to explicate two-phase flow and water removal inside cathode flow field from terrestrial gravity to microgravity. The cell was tested in the vertical and horizontal flow channel orientations. A 3.6 s short-time micro-gravity circumstance was provided by National Micro gravity Laboratory. Results show that gravitational level has an essential influence on gas-liquid two-phase flow characteristics for PEMFC with different configurations. The cell placed in different channel orientations also shows distinguished operating behavior because of the complicated impact of the changed gravity and configuration. Under the operating condition of a vertical flow channel orientation, accumulated water and droplets in terrestrial are pushed by oxygen flow to continuous removal toward the outlet of the fuel cell to alleviate water flooding, and the cell performance is slightly enhanced in a 3.6 s micro-gravity circumstance. Operating in a horizontal flow channel orientation, the generated water throughout the micro-gravity circumstance duration is not prone to move and flood flow channels in micro-gravity, meanwhile the cell performance is slightly deteriorated. (C) 2016 Elsevier Ltd. All rights reserved.