Abstract: In this paper, the essential of minimum zone straightness assessment is reconsidered from a mechanical point of view, and thus a mechanical model for straightness evaluation is built and the problem of the model is solved by using computational geometry, which is totally conformed to the minimum zone criteria.During the problem solving process of the model, a new parameterization method of line is introduced to overcome the illness problem of traditional method in numerical calculation.The validity of the proposed method is verified by comparing the evaluation results of two sets of data in a previous literature using the proposed method and other methods.