An improved multislice method is presented for performing dynamical calculations of high-energy electron diffraction and imaging in cases of inclined illumination. The method is shown by practical calculations to give results consistent with the traditional multislice method. The mathematical equivalency of the two methods for single-direction illumination cases is also given. However, there are some differences between the two methods for many-direction illumination cases such as in coherent convergent-beam electron diffraction (CBED). The improved multislice method may provide a more convenient expression for understanding coherent CBED problems and a more rapid algorithm for performing numerical calculations of the multislice approach in real space.