During the long range rocket flight, the rotation quaternion from the celestial system to the star sensitive coordinate system can be used as the input data for star map simulation. In this paper, starting from the definition of coordinate system, firstly, the practical engineering algorithm of Greenwhich Star Time Angle based on Beijing Time is improved. According to the principle of multiple rotations, the attitude conversion method from the celestial coordinate system to the launch inertial coordinate system is given; Secondly, the attitude conversion methods from the launch inertial coordinate system to the body coordinate system and from the body coordinate system to the star sensitive coordinate system are discussed; Finally, an example is given to verify the feasibility of the method. This method is easy to understand and can also be used to infer other cases according to derivation idea, which has certain reference significance of the attitude conversion in star map simulation.