Based on Hopkinson impact load theory, and taken into account the catenoid effect of mooring cable and revised the difference of tension and tangential direction action force by equivalent modulus of elasticity, the dynamical model of submerged monitoring platform on impacting and after impacting is formulated, which is aimed at impact tension of mooring cable and the dynamical response by the action of flow force. The equation is solved by hydraulics theory and structural mechanics theory of oceaneering, and the action force characteristic of mooring cable and motion characteristic of buoy are studied. The equation is calculated according to a specific example and hydrological environment. Through the result the conclusion can be got that the buoy will engender biggish heave and swaying displacement, but the swaying displacement gets stable quickly and the heaven displacement will produce vibration because of the vortex induced action by the flow. As the vortex induced action and the impact action between buoy and the mooring cable are existed, the tension changes greatly when the mooring cable is relaxation-tension.