The impedance measuring method may be used to assess the margin of breast cancer focus in the process of operation. This rapid measurement can shorten the waiting time and lighten patients’ pain in partial mastectomy. In order to satisfy the requirements of margin assessment, the design of electrodes structure is studied in this paper. Through simulation analyses on three types of the electrode structure, namely, strip-shaped electrode, square-shaped electrode and arc-shaped electrode, it is found that the arc-shaped electrode has better performances. The result of tissue experiments shows that the imaginary part of the impedance has more powerful character distinguishing ability.