Abstract: In order to study the coupling effect between the impeller and the casing profile of liquid ring pump on its performance, the profile of the blade and the casing were parameterized by using the high order Bezier curve and Direct Free Form Deformation (DFFD) method, respectively. A radial basis function (RBF) surrogate model was established for the relationship between the profile of the blade and the casing of liquid ring pump and vacuum degree and efficiency by using the LHS sample method. Multi-objective optimization was realized based on NSGA-Ⅱ algorithm. The optimization results show that the vacuum degree of the optimal model K( The optimal model for vacuum) is increased by 11.2%, and the efficiency of the optimal model J (The optimal model for efficiency ) is increased by 4.1%. The increase of the blade wrap angle and the expanding casing profile of suction section help to improve the vacuum of the pump inlet. The increase of outlet blade angle, the contracting casing profile of suction section profile would reduce the hydraulic loss and improve the pump efficiency. The comparisons of coupling optimization, independent optimization and step by step optimization of impeller and casing profile show that the coupling optimization results are obviously better than that of independent optimization. With the same surrogate model, the step by step optimization results of impeller and casing are basically consistent with the coupling optimization results..