The present invention relates to a jet pipe and its application method for cleaning under a flat vertical gate and a hydraulic underwater horizontal gate, and belongs to the field of fluid mechanics technology Background technology: The estuary area has a superior geographical location, abundant water resources and various products, and has always been a beloved habitat for humans. Humans have been breeding here for thousands of years, and through trade, shipping, and other means, the estuary area has gradually become the center of the economy. The population living here is large, and their daily lives and exchanges are extensive, gradually becoming an important gathering place and development area for human survival and development. In order to better utilize local resources and provide services for people in the estuary area, interception gates are generally installed at the estuary. In the early stage of water gate construction, it effectively accumulated moisture resistance, stabilized and improved the demand for land expansion in the upstream area of the river mouth, and made certain contributions to the development of industry and agriculture in the upstream area. But over time, sedimentation occurs under the water gates, with varying degrees of sedimentation at each river mouth, ranging from light to severe, and the sedimentation cannot function properly. The problem of gate sinking is becoming increasingly prominent, but the losses it brings are also expanding, which significantly restricts the development of the local economy. Therefore, various silt countermeasures have been developed. For example, hydraulic silt, artificial silt, ship silt, ship silt, tidal silt, cutting diameter, hydraulic pool, etc. Although these decontamination measures have achieved certain decontamination effects, they have also played a role in the current gate. Overall, these decontamination measures have the following disadvantages: 1. After the construction of the gate, the upstream flow rate decreases, the downstream flow rate decreases, and the water level difference between upstream and downstream decreases, which can ensure that soil and sand flow through simple downstream decontamination. 2. Cleaning machines and other measures consume a lot of manpower and financial resources, and the effect is temporary. It is necessary to work in a timely manner at any time, not a long-term plan. 3. Breaking the original cultural and ecological landscapes of the environment goes against the harmonious development required by local policies.