To provide higher measure precision of the star sensor attitude, the principles of error that appears because the three Euler angles are influenced by proper motion are studied in this paper. The proper motion level is divided into Ⅰto Ⅸ and stored in the guide star catalogue and the yearly variation of different star proper promotion in the last 20 years according to the output of three Euler angles is analyzed in depth. The simulation experiment results show that the precision can increase over 75″after adjusting the three Euler angles in the last 20 years by QUEST method. The new condition number can be minimized by choosing the star with relatively lower proper motion level to perform the calculation of the attitude when the magnitude of the stars is similar. This can improve the precision and stabilization of the star sensor attitude measurement greatly in the engineering.