This article describes a method for synthesizing an environmentally friendly overbased magnesium oleate detergent using oleic acid and active-60 magnesium oxide as materials. Reaction conditions including solvent, molar ratio of active-60 magnesium oxide to oleic acid, molar ratio of methanol to active-60 magnesium oxide, molar ratio of ammonia to active-60 magnesium oxide, addition mode of ammonia, carbonation temperature, molar ratio of injected CO2 to active-60 magnesium oxide, and CO2 rate were optimized. Under the optimized conditions, the overbased magnesium oleate detergent with a total base number (TBN) of 402 mg of KOH/g could be obtained. To improve the dispersing capability and the stability of the magnesium oleate detergent, the different dispersant/magnesium oleate mixed substrate detergents were synthesized using Tuwen-80, poly-12-hydroxystearic acid-pentaerythritol (PTHSAP), and poly-12-hydroxystearic acid-polyethylene polyamine (PTHSAPP) as dispersants.