In order to analyze the self-consistence characteristics of optical-axis perturbation due to the manufacturing error of monolithic crystal, mathematical model for the mirror tilt of the non-planar ring cavity has been developed and optical-axis perturbation is discussed by utilizing the augmented ray matrix formulation. The results show that: self-consistence of the optical-axis is not sensitive to distance deviation and it can be realized by designing the input-output coupling mirror to be a curved surface. Static analysis indicates that the optical-axis is still self-consistent for the plane input-output coupling mirror when the angles of two symmetric totally reflective planes satisfy the certain relationship. Besides, if the certain condition of the angles cannot be satisfied, steps to reduce the deviation of coupling point position are considered from aspects of making manufacturing error symmetrical and decreasing error. At last, dynamic analysis provides a much more reasonable method to explore the manufacturing tolerance, offering a theoretical guide for the experiment.