Underwater interfacing device of flexible manipulators is designed in order to avoid blindness and fatalness of direct interfacing and fit the condition of low visibility and large leaning swing. At initial stage of interfacing, velocity expression of single manipulator is obtained. According to position relation of interfacing device and aim circle, coordinate transforming matrix is obtained through analysis. Considering limiting relation of harmony movement, the method of Denavit- Hartenberg is adopted to get velocity expressions of two opposite manipulator ends. At pulling down state, reverse kinematical solutions of parallel mechanism are solved to obtain lengths of manipulators.