Abstract: The preparation process of calcium polyisobutylene thiophosphonate，including polyisobutylene thiophosphonic acid and calcium polyisobutylene thiophosphonate were developed. The reaction parameters for synthesis of polyisobutylene thiophosphonic acid, such as reaction temperature，reaction time，the dosage of P2S5 and catalyst，the dosage of water for hydrolysis were investigated. The optimized reaction parameters covered a reaction temperature of T0，a reaction time of 10 h，a mass ratio of P2S5 to polyisobutylene of 21%，a mass ratio of catalyst to polyisobutylene of 0.5% and a mass ratio of water to polyisobutylene thiophosphonic anhydride of 0.1%. The low basic calcium polyisobutylene thiophosphonate were synthesized by calcification process. The synthesis of polyisobutylene thiophosphonate in pilot reactor indicated that the preparation conditions were controllable with good test repeatability. The product, calcium polyisobutylene thiophosphonate, has a base value of 40-50mgKOH/g，while the mass fractions of P and S are greater than 0.9% and 3.0%, respectively. The product has good cleaning, dispersion and oxidation resistance, and can be used in internal combustion engine oil.

Key words: polyisobutylene thiophosphonic acid, calcium polyisobutylene thiophosphonate, engine oil, low basic