Square model post-processing includes DOC parts, DPF parts, mixers, SCR parts, and thermal insulation parts. It has the characteristics of compact structure, high conversion efficiency, low back pressure, convenient maintenance, low operation cost, and can effectively remove CH compound, particulate matter and nitrogen oxide in engine exhaust. Mixer components can provide good ammonia distribution uniformity, ensure that the conversion efficiency of each catalyst meets the requirements, effectively avoid urea crystallization; Thermal insulation parts ensure the internal catalyst working temperature requirements, to prevent high temperature damage of surrounding electrical components and personnel safety protection. Suitable for heavy duty vehicle aftertreatment system.