The bionic underwater thruster imitating fish's undulating motion can adapt its kinematic parameters to the changing of the flux and valve signal within its hydraulic system, so that it can generate a bionic motion smoothly, fluently and continually. In the paper, flux equations of the rotatable direction valve was built, as well as the dynamic model of the valve-controlled hydraulic swaying cylinder, with which the transmission function and Bode chart were produced. Some analysis were carried out on the valve-controlled hydraulic swaying cylinder, such as the stability, the dynamic rigidity of its position, and the dynamic response velocity. The results show that the valve-controlled hydraulic swaying cylinder is a stable system, and the response speed can be optimized by adjusting its structure parameters. However, its position rigidity can be affected by the frequency of disturbing load.