Abstract: In view of the inaccuracy and/or the unbearable calculation amount of the traditional method for checking the soft waveguide safety margin, we proposes a method based on the minimum radius of curvature. The feasibility, the convenience and the accuracy of the method are analyzed, and the specific calculation steps are given. Compared to the traditional method, the analysis results of a same example show that the proposed method can more accurately reflect the safety margin of the soft waveguide.