Abstract: In electron focusing and deflection systems the method of dynamic correction (i.e. the application of field curvature correction lenses and stigmators) can significantly reduce the overall aberration and greatly improve the optical properties of systems. In this paper the following numerical computation problems of dynamic correction are described: (1) the principle of correction lenses and stigmators; (2) the computation of field distributions in electrostatic and magnetic correction lenses and stigmators;(3) the calculation of the signal strengths applied in correction lenses and stigmators which completely cancel field curvature and stigmatism; (4) the effect of correction lenses and stigmators on distortion. From the examples of computation of dynamic correction given in this paper it can be seen that the dynamic correction plays enormous role in improving the electron optical properties.