Abstract: On the impact of the coordinate errors of the acoustic transducer on the positioning accuracy of the undersea geodetic control point, we proposed a joint adjustment method of the seafloor geodetic control point for GNSS/A underwater precise positioning, whose crux was treating the positions of both transducer and transponder as unknown parameters in the acoustic ranging equation. The paper further expounds the principle of the joint adjustment method, for the shortcomings in the proof of the superiority of the joint adjustment method and the lack of verification of deep-sea data, the strict superiority proof and the precision evaluation formula of the joint adjustment method are given in this paper. Using Songhua Lake data and South China Sea data for verification, the precision of seafloor geodetic control point positioning with the proposed method is improved by 2% to 26%. The application effect of the joint adjustment method in the lake area and the deep-sea area is shown.