Several results on optical-axis perturbation and elimination of the mismatching error C of a monolithic triaxial ring resonator (MTRR) are reported. Based on the augmented 5￡5 ray matrix method, by simultaneously considering axial displacement of a mirror and the misalignments in three planar square ring resonators of a MTRR, the rules of optical-axis perturbation are obtained. The mismatching error C of the MTRR is eliminated. The results obtained are important for cavity design, as well as in the improvement and alignment of MTRR.