With rapid progresses of the computer hardware and the development of high-powered computational techniques, the Computational Electromagnetics was born. As a newly arisen method, the Multidomain pseudospectral time-domain (MPSTD) algorithm, suffered the extensive concern in recent years, has become to one of the hot point directions of the Computational Electromagnetics.In this paper, the study of algorithmic theory and the study of engineering application are combined together to expand the application fields of the MPSTD algorithm. The main contributions of the author in the paper are outlined as follows:1. The calculating flow chat and various key techniques are summarized systematically and totally. The merits and disadvantages of the key techniques are analyzed and compared with each other.2. The MPSTD algorithm based on polar and cylindrical coordinates is studied. Firstly the principles and implementary steps of the MPSTD algorithm based on polar and cylindrical coordinates are put forward. The formulations of space differential coefficient are derived. Then the characteristic variables based on polar and cylindrical coordinates are proposed. Finally the numerical boundary conditions based on polar and cylindrical coordinates are studied. The corresponding formulations are derived for the fields updating. The numerical results indicate that the MPSTD algorithm based on polar and cylindrical coordinates is accurate and efficient, and the spending of calculate is reduced greatly.3. The CPML absorbing condition in polar and cylindrical coordinates is studied. The corresponding formulations are derived for the fields updating. The numerical results indicate that the CPML absorbing condition in polar and cylindrical coordinates is accurate and efficient, and the spending of calculate is reduced greatly.4. A new approach of source setting is proposed, which generates a unilateral wave in the waveguide. Firstly principle of this source is given. Then implementary steps and the corresponding formulations are proposed. Finally the unilateral characteristics are compared with the existing bidirectional source.5. Applications of mono-pulse slot antennas using the MPSTD algorithm are studied systematically. The characteristics of the three main parts of mono-pulse slotantennas——longitudinal radiating slot, center-inclined slot and magic T using couplingslot, are analyzed. Also the influence of the design parameters, such as the length and width of the slot etc., are analyzed. The engineering curves of design are given, and some beneficial conclusions are gained too. These also give powerful supports for the design of slot antennas. The numerical results indicate that the MPSTD algorithm is accurate and efficient to analyze mono-pulse slot antennas.6. Applications of some transmission-line and passive microwave components using the MPSTD algorithm are studied. The engineering curves of design are given, and some beneficial conclusions are gained too. This gives a new way to analyze the wide band characteristics of complex passive microwave component efficiently and exactly.