A water-jet machine includes a body having a passage defined therethrough and a plurality of piston devices disposed in a top thereof, a plurality of first holes defined through a lower portion of the body, a bar disposed in an underside of the body and having a plurality of fourth holes defined therethrough, two supporting plates disposed to an underside of the bar and having a gap defined longitudinally therebetween, a board disposed between the bar and the two supporting plates and having a plurality of apertures defined therethrough which communicate with the fourth holes, the first holes and the gap, and at least one transverse bar connected to the piston devices and connected to the two supporting plates by bolts extending through the body so that the board is securely positioned by actuating the piston devices to lift the transverse bar upwardly.