Finite element analysis is carried out to provide an engineering design approach of a newly proposed Triple-TEM cell (TTEM cell). Important characteristics such as characteristic impedance, TEM mode field distribution, as well as TE and TM modes cutoff frequencies can be analyzed by using the software developed in this paper. Design guidelines have been provided for the TTEM cell. Reasonable geometric structure of the cross-sectional area of the TTEM cell would thereupon be resolved. Numerical results of the local higher order modes along the length of the cell are presented in this paper.