A small floating surface is designed for the problem that a detection device works on the sea and is disturbed by waves. The platform is connected by a floating device and a main platform through a flexible cable. The stress condition of the platform under disturbance of random waves is analyzed and the motion equation is established. The multi-body hydrodynamic simulation software AQWA is used to analyze the rolling and pitch motion of the platform under three-level sea conditions, and the results can be described by response amplitude operator (RAO). We change the diameter of floating tube and the center of gravity of the platform, and compare the movement of the platform under different structure parameters. The results show that the platform resonates with the water body at water frequency of 1.0 rad / s, and the rolling RAO reaches 23, which is not conducive to the normal operation of the equipment. The influence of the height of the center of gravity on the amplitude of the rolling motion is much larger than that of the floating tube. When the height of the center of gravity is −2.0m and the diameter of floating tube is 2.8m, the optimum amplitude of the platform is 1.53°. The article can provide a theoretical basis for the further study of floating platform.