The invention discloses a ditch-type thickener with an inclined plate sedimentation promoting structure. The ditch-type thickener comprises a thickening pond, a sedimentation pond and a clean water pond which are sequentially and linearly arranged, wherein the three water ponds are arranged under the ground, and the upper parts of the ponds are provided with top covers; the thickening pond is deeper than other ponds, and a discharging hole is formed in the bottom of the thickening pond; the bottom of the sedimentation pond is provided with a mud removing valve, one end of the mud removing valve is communicated with the front end of the bottom of the sedimentation pond, and the other end of the mud removing valve is communicated with the lower part of the thickening pond and is led to the discharging hole; liquid at the upper part of the tail end of the sedimentation pond is led to a drain hole, and feeding holes are formed in the parts, close to the initial end of the thickening pond, of the top covers; and the sedimentation pond is internally provided with the inclined plate sedimentation promoting structure comprising inclined sedimentation plates which are distributed every other a certain distance along the water flow direction, and the inclined sedimentation plates are arranged in a way that the upper parts of the plates are backwards inclined along the water flow direction. By using the ditch-type thickener, tailings are subjected to concentration treatment, and meanwhile, the extruded clear water is discharged or recycled on site; and the thickener is simple in structure and capable of saving space and achieving the aim of saving electricity and water.