Abstract: A new-type of electromagnetic modeling technology for high power microwave (HPM) transmission and radiation structures with large electrical-size and thick radome is studied. Hybrid equations are established by combining mode-matching and integral equation method. Multilevel fast multipole algorithm and preconditioners are used to accelerate this method. Some numerical examples are given out to validate the accuracy and the applicability, including flare-angle-tapered feed horn, power-combined antenna, beam waveguide and beam-waveguide antenna system. Far-field patterns and near-field power density distributions are simulated. The simulation results show that this new technology can fit the boundaries and model the feeding mode accurately. Computer memory cost is reduced using this method. Applicability and ascendant of this method are validated. Some aspects which can be improved are also discussed in this paper.