The operation situation of the existing coal washing system of Shaping Coal Preparation Plant was introduced, classification experiment were carried out for the filtrate water of 337 and 338 small coal dewatering centrifuge, it concluded that the granularity grade in the filtrate water of the small coal dewatering centrifuge was greater than the overflow water of hydraulic classifier hydro-cyclone. In order to solve the problem of too large amount of slime treatment, the modification of filtrate water for 337 and 338 Small coal dewatering centrifuge was put forward, and a concrete plan for improvement of filtrate water diversion was designed. Through the evaluation of the technical indexes of the recovered coarse particles and the recovery rate of clean coal in the filtrate, the operation condition of the coal washing system after modification was obtained. The results show that the reformed coal washing system has the characteristics of less slime production, less consumption of flocculant, recovery of coarse slime, lower production cost and better recovery of clean coal.