Experimental study of matrix carbon field emission cathodes (MCFEC), which has led to stable operation of the cathodes with emission current value up to 100 mA, described. A method of computer-aided design of TWT electron guns.(EC) MCFEC, based on the results of the MCFEC emission experimental study, Is presented The experimental MCFEC emission characteristics are used to define the field coefficient K and cathode effective emission area Seff. The EG program computes th electric field upon the MCFEC surface multiplies it values by the K value and F-N law and the Seff value to calculate the MCFEC current; the electron are computed as well.