For preparing cryogel beads by the micro-flow-focusing and cryo-polymerization method, liquid-liquid flow patterns and slug characteristics for the system of Dex-MA and ethyl acetate and the system of Dex-MA-HEMA and ethyl acetate in a cross-shaped square microchannel were studied. The aqueous solutions of Dex-MA-HEMA and Dex-MA were used as the dispersed phase and ethyl acetate as the continuous phase. The formation mechanism of the slug flow was illustrated by analyzing the interaction of the interfacial tension between the dispersed and continuous phases, inertial forces and viscous forces of the dispersed phase and the continuous phase. The flow pattern maps for the two systems were proposed and five regimes were identified, i.e., the slug flow, bubbly flow, jetting flow, unstable flow and stratified flow. The slug lengths and the droplet diameters were also measured experimentally and correlated. The results showed that the formation of the slug flow was related to the interaction of the forces of the continuous phase and dispersed phase. The inertial and viscous force of the continuous phase promoted while the viscous force of the dispersed phase resisted the formation of the slug flow. The interfacial tension and the inertial force of the aqueous phase were shifting their effects which either promoted or resisted the formation of the slug flow. The flow pattern maps have a good agreement with those proposed in the literatures. The velocity of the continuous phase was more influential on the length of the slug segment. The obtained correlation of slug length and the droplet diameter could be helpful to the preparation of the cryogel beads. (C) 2019 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.