Geomats are widely used for erosion control on slopes, yet quantitative links between their structural characteristics and erosion resistance remain insufficiently understood. This study investigates the influence of geomat geometry on erosion mitigation of silty slopes reinforced with five geomats. Erosion tests under simulated rainfall were conducted. An integrated structural-hydraulic-erosion framework was applied to relate geomat structural parameters, including porosity, pore-structure characteristics, compressed thickness, and mass per unit area, to hydraulic indicators (surface flow velocity and kinetic energy of surface runoff) and erosion indicators, including collected runoff mass, soil loss, sediment concentration, eroded area fraction, and maximum connected erosion area fraction. The results show that geomats substantially reduced erosion relative to the bare slope, decreasing cumulative soil loss by up to 89.1 %, sediment concentration by up to 84.3 %, and kinetic energy of surface runoff by 87.7-95.2 %. Geomats reduced erosion-domain connectivity and inhibited the development of continuous scouring channels, indicating effective attenuation of near-surface hydraulic forcing. Porosity and compressed thickness emerged as the dominant structural controls on erosion resistance. Geomats with porosity <= 26 % and compressed thickness >= 16 mm exhibited the best performance under the tested conditions. These findings provide mechanism-informed, preliminary guidance for erosion control on geomat-covered silty slopes.