To investigate the effect of CaCO₃ concentration and velocity on CaCO₃ scaling fouling process on plain,straight oblique and saw-tooth oblique fin tubes,experiments were done at different CaCO₃ concentration,velocity and surface parameter of the three kinds of tubes.The results show that the homogeneous nucleation rate and the growing rate both increase when CaCO₃ concentration increases.This makes the scaling particle concentration and fouling ion concentration increase,the former leads to more scaling on tubes and the later enlarges the heterogeneous nucleation rate and growing rate.Higher velocity decreases the nucleation of scaling,scaling crystal and fouling resistance,but it can prolong the induction period.Higher velocity increases nucleation rates on straight oblique fin tube and saw-tooth oblique fin tube,but the induction period extends and the mass of scaling and fouling resistance decrease.Straight oblique fin tube and saw-tooth oblique fin tube have bigger heat transfer coefficient than plain tube under both clean and fouling conditions in despite of smaller fouling resistance and a little more scaling.Under the same condition,saw-tooth oblique fin tubes have bigger heat transfer coefficient and fouling mass than straightoblique fin tubes,but the total heat transfer coefficient is bigger than that of straight oblique fin tubes.