Polymorph screening is extremely critical in the research and development of pharmaceuticals. In this study, an easy-to-use microfluidic device was developed for the antisolvent crystallization of L-glutamic acid to create complex supersaturation gradients along the microchannel, which could contribute to the polymorph screening process. The effects of factors including temperature, initial concentration, and flow rates on the polymorph selectivity of L-glutamic acid were investigated in the binary solution system of water and ethanol. Powder X-ray diffraction as well as scanning electron microscopy was used to characterize the polymorph and morphology of the obtained crystals. The experiment results demonstrated that crystals of both the metastable form alpha and the stable form beta were obtained successfully by adjusting different operating parameters. Meanwhile, it was found that the relative flow rate between solution and antisolvent and initial concentration of the solution were the predominant factors in the polymorph selectivity.