The invention discloses a method for processing monohydrallite ore washing gangue. The method includes: conveying first monohydrallite ore washing gangue to an efficient thickener so as to perform first concentration sedimentation on the first monohydrallite ore washing gangue, and first concentration underflow can be obtained; the first concentration underflow can be collected and mixed with second monohydrallite ore washing gangue to be conveyed to the efficient thickener, second concentration sediment can be performed, and second concentration underflow can be obtained; the second concentration underflow can be conveyed to a filter press for filter pressing, and solid-liquid separation can be obtained. The method for processing monohydrallite ore washing gangue is easy and convenient, fast, efficient and less in energy consumption, does not need to add additional devices compared with a conventional method, requires low cost, is good in solid-liquid separation effect, can fully recycle water in the gangue, accordingly can effectively save water resources and avoid environment pollution, and is particularly suitable for processing the monohydrallite ore washing gangue which is tiny in granule, large in viscosity, not apt to settle and difficult to process by adopting a conventional method.