Abstract: In order to solve the limited processing range of the electron beam manufacturing equipment and reduced processing accuracy at the edge of large workpieces, the defocusing and astigmatism of the electron beam at large deflection angle were studied. The aberration theory was used to analyze beam size increasing and shape distortion during electron beam deflection. A control system was set up to dynamically adjust the current of the focus coil and the astigmatism coil, that is,dynamic focusing and astigmatism elimination. Then a focused astigmatism correction table was made to reduce beam spot size of the electron beam within the whole field. Then, the secondary electronic imaging method and EOG（energy of gradient）evaluation function were used to verify the correction effect. The experimental results show that dynamic focusing and astigmatism elimination can effectively improve the beam spot quality. After correction, the electron beam can have a clear image within 12°, and the EOG value of the electronic image is increased from 0.81 to 1.