DG Tau is a nearby T Tauri star associated with a collimated jet, a circumstellar disk, and a streamer a few hundred au long. The streamer is associated with an SO emission at one end, which suggests that the streamer is an accretion flow onto the disk around DG Tau. We demonstrate the validity of this scenario based on hydrodynamic simulations, considering a cloudlet initiating infall at 600 au from DG Tau with low angular momentum so that the centrifugal force is smaller than the gravitational force, even at 50 au. The tidal force of DG Tau elongates the cloudlet into a streamer. Our hydrodynamic model reproduces the morphology and line-of-sight velocity of the red-shifted CS (5-4) emission from the streamer observed with ALMA (Garufi et al. 2022). We discuss the conditions for forming a streamer based on the simulations.