Copper slag produced during copper smelting contains Fe, Cu and other valuable metal elements. It is need to recover valuable metal from copper slag for resource utilization value and protecting the ecological environment. Usually, oxidation modification treatment is needed before recovery the valuable metals from copper slag,but, Iron grade of oxidation modified copper slag is low, content of SiO2 is high, and further treatment is needed. The purpose of this paper is to explore the effect of flocculation and reverse flotation process on the reduction of silicon. The experimental study on the flocculation and reverse flotation of the oxidation modified copper slag, the optimum conditions for the flocculation reverse flotation process were determined: humic acid sodium(2%)2.0mL,pH=9,starch (4%)4.0mL, laurylamine(2%)1.0mL. Iron grade of the iron concentrate that we get from this experiment is 52.84%，Si content fell to 7.88%, iron recovery rate of 78.35%.