This article presents a method for synthesizing an environmentally friendly composite-metal (calcium and magnesium) oleate detergent, using oleic acid and composite alkaline salts (Ca(OH)(2) and active-60 MgO) with high activity and reactivity as raw materials. Reaction conditions, including the molar ratio of composite alkaline salts (Ca(OH)(2) and active-60 MgO) to oleic acid, the molar ratio of xylene to composite alkaline salts (Ca(OH)(2) and active-60 MgO), the molar ratio of methanol to composite alkaline salts (Ca(OH)(2) and active-60 MgO), the molar ratio of ammonia to composite alkaline salts (Ca(OH)(2) and active-60 MgO), the molar ratio of injected CO2 to composite alkaline salts (Ca(OH)(2) and active-60 MgO), and CO2 rate, were optimized. Using the optimized conditions, a high-alkali composite-metal (calcium and magnesium) oleate solution with a total base number (TBN) of 316 mg KOH/g and an overbased composite-metal (calcium and magnesium) oleate solution with a value of TBN = 412 mg KOH/g could be obtained. In addition, the relationship between the TBN of the product and the metal content (calcium and magnesium) also was discussed.