The application of variable axis lens (VAL) technology to high-resolution electron microscopes has been well established. In the present study, a focusing-deflection composite system of space electron beam guns is designed based on the curvilinear variable axis lens (CVAL) theory to achieve the effective deflection of electron beam guns for welding in space. In addition, the conditions for the curvilinear variable axis of the focusing-deflection composite system combining a magnetic lens and electrostatic deflectors are deduced, and a curvilinear optical axis combining two parabolas is introduced as the designed trajectory. Finally, through the adjustment of the stimulation and angle of the deflectors, a function of the deflection field in line with the design requirements is obtained. The focusing-deflection composite system of space electron beam guns designed in this paper, consisting of two deflectors, is shown to meet the technical requirements for welding in space, and the deflection radius can reach up to 5 mm when the conditions for the curvilinear variable axis have been met.