The present invention provides a method of obtaining a classification boundary, to limit an axial depth in a puncturing operation. The following steps of method comprises: At first, obtaining a plurality of tomographic images from the axial depth of a tissue is performed. Then, obtaining a plurality of characteristic values from the tomographic images, the characteristic values are classified by a Support Vector Machine method. A classification boundary will be obtained through a distribution of the graph for defining a specific compartment of the tissue. In addition, an automatic recognition method and system using the above mentioned method are also disclosed in the present invention.
