Abstract: To address the limitation that the quality of simplification of a depth-contour in nautical chart can only be analyzed qualitatively, not quantificationally, these indices including the contour length of extending deep area, the mean distance of extending deep area, the reducing deep area, the curvature and the dispersion to a smoothed curve are defined, respectively from the safety of navigation, the representation of available depth space and the smoothness, the corresponding evaluating methods are proposed, and the indispensable formulas are concluded. The experimental results demonstrate:(1) the defined indices can effectively and reasonably estimate the quality of simplification of depth-contour in nautical chart from the safety of navigation, the representation of available depth space and the smoothness; (2) the proposed methods can estimate the quality of depth-contour simplification and overcome the shortcoming of the existing methods which can only analyze qualitatively.