Abstarct: Abstract Due to the fact that Qeshlaq coal washing plant is a traditional plant, it is only able to wash coarse grain coal and it is not possible to wash fine coal (below 5mm). Therefore, the purpose of this study was to design a fine washing circuit (flotation and spiral) for washing fine coal in Qashlaq coal washing plant to increase the production capacity and quality of the coal output of the plant. To achieve this goal, the response surface method of designing experiments was used to evaluate and optimize the parameters affecting ash and weight recovery of coal. The results showed that among the effective parameters, the amount of frother agent had the most influence on the ash reduction and solid content on the coal recovery. Increasing the solid percentage, the amount of ash was increased significantly; so that with a solid content of 30%, the amount of ash was 9.3%, and while solid content of 8%, the amount of ash decreased to 4.7%. In the solid content of 20%, the highest amount of ash reduction was observed in the low dose of the collector (80 g/ton) and high dose of frother (80 g/ton). The highest amount of ash reduction was observed in high amounts of frother and low content of solids. So that with the solid content of 10% and increasing the frother from 40 to 80 grams per ton, the ash was about 5%. In optimal conditions, the least ash (about 5.17%) was obtained with 167 grams per ton of collector, frother dose of 70 grams per ton and solid content of 10.2%.