Cathode current is a key measure of the rated power of the diode and is closely related to the cathode structure. Compared with $\Pi $ cathode and helical cathode, the mesh cathode has been more widely used in high-power tetrode, because of its structural advantage. So far, the relationship between the space charge limited current (SCLC) and the cathode structure for thermionic emission mesh cathode diode has not been reported. In this article, we develop a calculation expression of the SCLC for the mesh cathode coaxial cylindrical diode, which is based on the calculation model of the helical ...