Most of stone cutting factories are placed in dry region. The required water of these factories is provided by digging deep wells. To reduce water consumption, often the obtained wastewater is treated in traditional way through sedimentation basins at low efficiency. Recently, the use of hydrocyclones to treat with high efficiency has increased, it is important to know the factors affecting the improvement of treatment efficiency. In this study, the effect of parameters including input flow rate, inlet pressure and retreatment of the overflow on the performance of a 140mm diameter hydrocyclone were investigated. Experiments were designed with the aim of separating granite and marble powder particles using the “Response Surface” method by DESIGN EXPERT. 10 software. A according to the obtained results, by increasing the input flow from 0.7 to 1.3 Li/s and reducing the inlet pressure from 4.1 to 2.1 bar, the separation efficiency of granite and marble in the first stage of treatment, respectively 11.19 and 15.04 %, and in the second stage, 6.84 and 12.23 % has been increased. Also, the retreatment of the overflow from the hydrocyclone increased the total separation efficiency for granite and marble wastewater by 16.24 and 15.16 %, respectively. Due to the high price of water supply in these factories, changing the input flow rate, pressure and the retreatment of the overflow of the first stage of treatment without the need to add a hydrocyclone and other equipments, it is suggested to improve the treatment efficiency.