The invention discloses an automatic slope cropland runoff water collection device which comprises a runoff water collection tank, a tank cover and a monitoring component, wherein the tank cover is used for sealing the runoff water collection tank; the monitoring component is used for monitoring runoff water flow inside the tank. As a handle for lifting up the tank cover is arranged on the tank cover of the automatic slope cropland runoff water collection device disclosed by the invention, a large-size tank can be successfully opened or closed by a single operator in outdoor operation; due to the adoption of a sealing ridge on the tank cover, deposits outside the device can be prevented from falling into the tank in the runoff water collection process or the water sample collection process, and external impurities, dust, insects and waterfall which do not pass through a runoff cell are prevented from entering the collection tank to contaminate runoff water inside the tank; by adopting the device disclosed by the invention, runoff water of various landform areas such as croplands, mountainous regions, terraced fields, tailings and barren mountains can be automatically collected and monitored, therefore, reliable data and uncontaminated sample resources can be provided for multidisciplinary studies such as conservation of water and soil, non-point source pollution prevention and control and nutrient loss control.