The invention belongs to the field of hydraulics experimental models and particularly relates to an automatic gantry type gate used for simulating the instantaneous dam break. The automatic gantry type gate comprises a gantry type support, a gate plate located below the gantry type support and a gate plate lifting control device. The gate plate lifting control device comprises a first weight block matched with a vertical guide rail fixedly connected to the gantry type support, and a lifting motor controlling the first weight block to ascend and descend. The gate plate is connected with the first weight block after being connected to a pulley block arranged on the gantry type support in a winding manner through a steel cable set. The gantry type support is fixedly provided with a fixing plate provided with a guide groove. The guide groove slides vertically in cooperation with a vertical guide bar arranged on the gate plate. Sealing buffering bars are arranged on the edges of the two sides of the gate plate and at the bottom end of the gate plate correspondingly. The first weight block is controlled to ascend and descend through a lifting motor controller, and therefore the gate plate is controlled to ascend and descend. The automatic gantry type gate can be automatically started and reset and is suitable for various sizes of water tanks, time and labor are saved, and errors can be effectively reduced.