In this study, soils with different bulk densities and textures from the black soil region of Northeast China were investigated. Soil samples impregnated with acetone-diluted unsaturated polyester resin (UPR) at dilution ratios of 0%, 70%, 80%, and 90% were compared through observation under a stereo microscope (10×magnification) and a polarizing microscope (100×magnification). Based on the observations, evaluation criteria for impregnation effectiveness were established, and optimal impregnation protocols for soils with different bulk densities and textures were determined. The results demonstrated that qualified micro-morphological samples should exhibit good cutting integrity, surface damage resistance, and pore-filling completeness when observed under a stereo microscope. For optimized soil impregnation protocols, bulk density-specific selection dictated that soils with bulk density >1.70 g/cm³ or within 1.40-1.50 g/cm³ should utilize 191^# UPR diluted with 90% acetone, while those with bulk density <1.20, 1.30-1.40, or 1.50-1.70 g/cm³ required 80% acetone-diluted 191^# UPR, and soils in the 1.20-1.30 g/cm³ range should employ neat 191^# UPR. Texture-dependent optimization specified that silt-textured soils need 196^# UPR diluted with 90% acetone, silty loam and loam-textured soils necessitate 80% acetone-diluted 191^# UPR, and sandy loam-textured soils should use undiluted 191^# UPR. In conclusion, these methods can enhance sample preparation efficiency and improve section quality score, thus can provide methodology for high-quality soil micro-morphology analysis, critically advancing mechanistic understanding of impediment layer development in Mollisols in northeast China.