A new algorithm which is “the minimum zone evaluation for sphericity error based on the dichotomy approximating” has been presented with the geometric characteristics and research situation of sphericity error and through the understanding of the definition and the evaluation problem of the sphericity. The principle of the algorithm is that based on finding the initial point of the ball as the base, around which the side decorates cube by certain length, calculating the distance of the points on the sphere to the cube measuring points of the eight vertex and the initial point, by comparing and judging to find a new beginning starting point, and arrange new cube repeatedly until meets the requirement. The sphericity error value of corresponding evaluation method (Minimum Zone Sphere method (MZS)) was obtained according to that. The mathematical formula、program flowchart and example verification were given. The example verification results show that the sphericity error can be evaluated effectively and exactly with this algorithm.