Technology that prepared iron oxide red pigment from the separator liquid between iron and aluminum of coal gangue was optimized though response surface experiment design based on the purpose of coal gangue resource about efficient utilization. The effects of Na₂CO₃ concentration, reaction temperatures and Fe(II) concentration on the purity of the iron oxide red pigment were researched. The response surface experiment design was employed to optimize based on the single factors experiments, phase structure from products and microstructural aspects were analyzed. The results indicated that the purity of the iron oxide red pigment can be reach to 96.09% when Na₂CO₃ concentration was 107 g/L, reaction temperature was 43℃and Fe(II) concentration was 0.26 mol/L. The purity and other indicators could meet the requirement of a kind iron oxide red from standard specifies iron oxide red pigment GB/T1863-2008. The intermediate products was a-FeOOH and g-FeOOH with obvious needle aspects and that disappeared by calcination then a-Fe₂O₃ withbetter crystalline was obtained.