Abstract: In view of the fact that the rolling and pitching of the carrier platform of half-rotating impeller tidal turbine (HRITT) has great influence on the hydrodynamic performance of the turbine, a catamaran floating platform was designed as the carrier platform of HRITT. The allowable angle ranges of the rolling and pitching of turbine were calculated with the method of computational fluid dynamics. Based on the frequency response method, the theoretical analysis model of amplitude response operator (RAO) of the platform rolling and pitching was established, and the RAOs of rolling and pitching of platform were calculated. The validity of theoretical model was verified by comparing the results of RAO theoretical model and numerical simulation. Taking the RAO rolling and pitching of the platform as the objective function, the size constraint and the stability of the platform as the constraint conditions, the multi-objective optimization design of the main scale parameters of carrier platform was carried out. The results show that the allowable rolling angle of HRITT is from 0° to 8°, and allowable pitching angle of HRITT is from 0°to 12°. After optimization, the maximum roll angle and pitch angle are 7.49° and 8.78°respectively, which are within the allowable range of rolling and pitching angles of HRITT. The RAO reduction of rolling and pitching are 49.36% and 42.46% respectively, which can ensure the efficient operation of HRITT.