The invention relates to a preparation method of an organic pigment, in particular to a preparation method of a low-arsenicred iron oxide pigment. the method produces a low-arsenicred iron oxide pigment by a two-step oxidation liquid-phase production method and does not use sheet iron in two-step oxidation, thereby reducing the consumption of sheet iron resources and obtaining iron red with better fineness and dispersion than those of iron red produced by a sheet iron mixed acid method. Because the sheet iron is not used in the two-step oxidation, the contents of heavy metals, such as arsenic, lead, and the like can be effectively controlled. The low-arsenicred iron oxide pigment prepared by the method contains As not more than 5 mg/kg and Pb not more than 10 mg/kg. The invention can be widely applied to industries, such as pencils, toys, cosmetics, medicine, tipping paper, and the like.