Abstract: For high efficient EM simulating requirements around FLAPS-typed HPM transmitters based on spatial power combination techniques, integral equation methods (IE) accompanied with multi-scale geometrical and EM modeling techniques named MLFMA-MLACE are applied in this paper. The algorithms mainly concern multi-scale geometrical modeling for the designed project, MLFMA acceleration in macroscopical layer and adaptive MLACE acceleration in microcosmic layer. Through some primary applications in W-band FLAPS models, the precision of the combined methods is validated. Its applicativity, approximate level in detail, effects and computational cost are sufficiently analyzed. The results show that as to aspects of memory requirements and computational time, the combined technique has extremely evident advantage. Some discussions about future improvement are also given in this paper.