Abstract: An additive package for 70TBN marine cylinder oil was developed using high base number calcium naphthenate T114 as main metal detergent, then 70TBN marine cylinder oil was produced with said additive package. The physical and chemical properties of the prepared cylinder oil were tested and simulating performance evaluation was carried out using similar imported product as reference oil. Test results showed that the qualities of prepared cylinder oil and reference oil were at the same level, indicating that the prepared additive package could meet the demand of blending 70TBN marine cylinder oil. Moreover, this additive package exhibited good adaptability to various type I and type II base oil products (domestic and abroad) for blending qualified 70TBN marine cylinder oil. The commercial trial of producing said additive package showed that the reproducibility was excellent, and the prepared cylinder oil product having stable quality.