Straight-through microchannel (MC) emulsification enables formulating monodisperse emulsions using a channel array vertically microfabricated on a plate surface (a straight-through MC). This study investigated the effect of the fluid flow in a channel on the generation of soybean oil-in-water emulsion droplets from an elliptic channel using Computational Fluid Dynamics (CFD). The visualized CFD results demonstrated that droplets with diameters of 32 to 38 μm were stably generated from the channel below the critical flow velocity of the to-be-dispersed phase (U_d). Above the critical U_d, we observed a drastic increase of the resultant droplet diameter. The calculated droplet generation rate achieved a maximum value of about 15 droplets per second at the critical U_d. An analysis of the neck formed inside the channel during droplet generation explained why the droplet generation behavior from the channel drastically changes over the critical U_d. The CFD results obtained in this study were confirmed by our experimental results reported in the literature.