Multipactor is a critical physical issue leading to performance degradation or even failure of space high-power microwave systems. This phenomenon typically occurs inside microwave devices, where free electrons resonate under continuous acceleration by radio frequency electric fields and undergo electron multiplication via secondary electron emission processes, ultimately triggering multipactor. This effect not only degrades component performance but can also cause failure of components or even entire spacecraft in severe cases. Dielectric microwave components, known for their high Q factor, low loss, and ease of miniaturization, are increasingly employed in space microwave systems. While the introduction of dielectric materials significantly enhances certain performance aspects of components, it also adds complexity to multipactor analysis to some extent. Unlike metallic components, when electrons collide with dielectric surfaces, they may accumulate a layer of positive or negative charges on the surface. The resulting quasi-static electric field, combined with the microwave electric field, influences the trajectory of electrons. In this work, by taking microwave ridge waveguide devices filled with polytetrafluoroethylene and polyimide as the research objects, we conducted device design, modeling, and multipactor threshold research. It analyzed the physical mechanism by which microporous structures on the surface of multipactor-sensitive areas in the device reduce the surface secondary electron emission capability. The study demonstrated that constructing microporous structures on the dielectric surface in discharge-sensitive regions can effectively reduce the secondary electron yield and significantly enhance the device's multipactor threshold. Periodic microporous arrays were fabricated on PTFE and PI surfaces using femtosecond laser processing technology. Morphological characterization, SEY testing, and multipactor threshold simulation analysis showed that the peak SEY of PTFE decreased from 2.1 to 1.4, a reduction of 33.3%, while the first crossover energy (EP1) increased from 40 eV to 95 eV. For PI, the peak SEY decreased from 1.4 to 1.1, a reduction of 21.4%, and EP1 significantly increased from 65 eV to 205 eV. The microporous structure raised the multipactor thresholds of PTFE- and PI-filled single-ridge waveguides to 12374 W and 12109 W, respectively, representing an improvement of approximately 5000 W compared to untreated surfaces. This research provides an effective technical approach for microstructural treatment of dielectric surfaces in high-power microwave devices, and holds significant engineering application value for anti-multipactor designs in various microwave systems.