This paper studies the performance analysis of the multiple USVs' cooperative localization system based on the relative distance measurements with a single leader under different maneuver conditions. In order to analyze the performance of the cooperative localization system quantitatively, a new cooperative coordinate is established and motion models of the leader and follower USVs are derived. Furthermore, the USV cooperative localization system's observability and the degree of observability is analyzed. In addition, aiming at unobservable paths, a method about changing control input is proposed to improve the degree of observability. Through MATLAB simulation experiment and water experiment results show that under different conditions, by adjusting the control input method to change the system observability is effective. And the results show that the analysis method proposed in this paper can reflect the positioning performance of cooperative positioning system, verify the effectiveness of this method.