In this work, we generated gas-in-water-in-oil (G/W/O) multi-cores double emulsions with a one-step microfluidic device and found a new stable flow pattern, where multi-cores double emulsions were easily fabricated. The mechanism of the particular flow pattern was discussed. Moreover, we systematically studied the effects of the three flow rates on the size and structure of the double emulsions. We then developed mathematical models to predict the size and structure of the double emulsions. On this basis, porous polyacrylamide hydrogel microspheres were successfully fabricated by in situ UV polymerization method. This method provides a simple and novel approach to produce porous microspheres. (C) 2014 Elsevier B.V. All rights reserved.