Abstract: The chemical composition of separating ring and concasting process have been improved by analysis on break of separating ring for horizontal concasting φ130 mm billet for tube and test of effect of separating ring composition on properties. The results showed that with using B-Sis N₄₊ 30% BN separating ring, manufactured size precision of separating ring up to 0.1 mm, controlling [N] no more than 60×10^-6,[O] no more than 30×10^-6 and reverse bush between 3 mm and 5 mm, the break of separating ring was controlled effectively ,the average break ratio of separating ring per month de- creased to less than 0.3% from original 8.3%.