Micro mixers are good platforms to realize liquid liquid mixing, but they still need intensification when treating extreme flow conditions, such as relatively higher fluid viscosity than water (mu > 3 mPa s) or high flow rate ratio (R > 10). In this work, the quantitative mixing enhancement rules with inert gas phase as enhancing medium in three typical micro mixers, T-junction microchannel, cross junction microchannel as well as co flowing microchannel, are experimentally studied using "Villermaux-Dushman" parallel competitive reaction. The results show that the gas makes Xs reduced by 2-5 Limes in the working systems with various viscosities (0.86 mPa s <= mu <= 11.46 mPa s) and operated in a wide range of flow rate ratio (1 <= R <= 25) The mixing enhancement mechanism is the two phase segmented flow and we find only 0.05-0.1 gas liquid phase flow rate ratio (R-gas) is enough for the gas phase to develop its enhancing effect. Based on the characteristics of segmented liquid flow, a mathematical model is established to predict the variation of Xs in three micro-mixers. (C) 2015 Elsevier Ltd. All rights reserved.