A marine lubricating oil composite additive is provided. Based on the total weight of the composite additive, said marine lubricating oil composite additive comprises: 25-45% sulfonate detergent with superhigh base number, 40-60% phenolate detergent with low base number, 0-8% dispersing agent, 0-4% antiwear agent, and 10-20% Group I base oil with high viscosity index which is selected from the group consisting of 400SN, 500SN and 600SN. The composite additive of the present invention can satisfy the requirement of BOB system about the viscosity and base number, and can be blended with many system oils under a number of domestic and foreign brands so as to provide cylinder lubricating oils with different base numbers. The composite additive of the present invention has good adaptability and excellent performances in terms of antiwear, antioxidization and high temperature detergency, which meet the requirement of marine engines about the performance of cylinder lubricating oils.