A hydrodynamic water blocking device for an underground garage includes a water blocking plate assembly and side rail assemblies, wherein the water blocking plate assembly includes a first water blocking element, one end of the first water blocking element is rotationally connected with a base, the other end of the first water blocking element is rotationally connected with one end of a second water blocking element, the first and second water blocking elements have foamed layers, the base has grooves capable of accommodating the embedded foamed layers, water inlets formed in the base communicate with the grooves, each of the side rail assemblies includes a side plate with an ascending rail including a horizontally disposed linear rail and an arc-shaped lifting rail, the second water blocking element has a walking assembly embedded in the ascending rail which is connected with a driving mechanism installed at the second water blocking element.