Abstract: The relationship between geodetic coordinate system and ship coordinate system is analyzed, the three-shaft-stabilized system’s attitude angles of the ship-borne radar in ship coordinate system are defined, when the value of platform compass and the ship-borne radar antenna’s attitude angles are given. A way to the three-shaft-stabilized system’s steady-state equations is provided by use of space analytic geometry method, which provides a theoretical basis for the serve control of the three-shaft-stabilized platform.