Abstract: This paper describes a method of the design of the transition region of the electron beams from partially shielded cathode. This method is applicable to magnetic focusing structures of the axisymmetric high-density electron beam. Through synthetical choice of the parameters of a magnetic system and an electron gun, a optimum matching between the magnetic and the electron gun is obtained. So good results are given: a shielding coefficient Kc is higher than 0.8, a ripple ratio of the electron beams is less than 0.01.