In view of searching the ideal cone axis for error evaluation of the conicity, a new kind of algorithm of evaluating conicity error, named as mesh searching algorithm, and the mathematical model of conicity error were presented. The algorithm has three steps. Firstly, a certain length square was collocated around the centre of least square circle on the initial section and terminal section. Secondly, a series of mesh points on the initial section and terminal section could be obtained by dividing the certain length square. And a series of lines could be obtained by connecting each mesh point on the initial section to the each mesh point on terminal section. Thirdly, a series of lines were regarded as theoretical cone axis, then the minimum zone conicity error could be calculated according to the definition of conicity error. The principle of the method and the steps of using the mesh searching algorithm to solve the conicity error were described in detail. Results of the calculation example revealed that the conicity error could be evaluated effectively and accurately by using the mesh searching algorithm.