Abstract Flow regimes of two immiscible liquids at the cross junction within a rectangular microchannel are experimentally investigated. Characteristics of the flow regimes including the critical conditions and interfacial deformations are presented. It is found that the occurrence of the tubing regime is favored by increased viscosity of the dispersed phase or reduced cross-sectional aspect ratio, leading to the shrinkage of the flow rate range that could produce droplets. In order to reveal the physical mechanism, the force analysis is carried out based on the tunnel structure formed between the interface and channel side walls within the rectangular cross-section. The reshaping stage and pinch-off stage are mainly driven by the interfacial tension, leading to far larger neck thinning rate compared to the superficial velocity of either phase. The filling stage and squeezing stage are dominated by the pressure drop across the dispersed tip while the role of the shear force becomes more important with increasing tunnel width. The filling period is estimated as t2≈kHwn02/Qd with k=1.34 and the squeezing period is expressed as t3/Tc=0.3Cac-1. According to the force analysis, the critical tip velocity under dripping scales with three key parameters, which can be expressed as (utip/U)*~QcLtip/wtunnel3.