Adjustable automatic farmland drainage valve

The invention discloses an adjustable automatic farmland drainage valve and relates to the technical field of agricultural irrigation and drainage. A filter screen, a water level adjusting button, scale lines and a drainage port are arranged on the front side of the drainage valve. The filter screen is mounted at a water inlet in the lower end of a floater so as to prevent suspended matters from entering the drainage valve and affecting the drainage valve; the water level adjusting button is adjusted manually so as to set a farmland water level control condition. The drainage valve can automatically and accurately control the drainage depth of the water layer of farmland to prevent the disaster that crops are waterlogged due to excessive water in the farmland, and meanwhile, the drainage valve avoids artificial guard under the condition that the rainfall intensity is higher and a waterlogging disaster is easy to generate, so that the drainage efficiency is greatly improved.