The invention discloses a star sensor non-high-frequency error on-orbit modification method, which comprises the following steps of S1, calculating the attitude quaternion qbo of a theoretical satellite body coordinate system relative to an orbit coordinate system (as a formula shown as the accompanying drawing); S2, for the star sensor attitude determination, the installation constant value error item qerr1, the effective load constant value deviation error item qerr2 and the effective load constant value period error item qerr3 are respectively introduced, so that the attitude quaternion qbo meets the formula shown as the accompanying drawing; S3, a rolling offset angle phi c0, a yawing offset angle theta c0 and a pitching offset angle psi c0 are set; during the on-satellite attitude calculation, the uncertain constant value attitude angle deviation is corrected according to the offset angles, so that the final attitude determination angle is corrected. The star sensor non-high-frequency error on-orbit modification method has the advantages that the system attitude determination precision is greatly improved; the powerful support is provided for the high-precision imaging of the effective load.