Abstract: Development and validation method of a selective catalytic reduction（SCR） mixer was proposed for diesel engine after-treatment system deposit risk control to meet China Ⅵ emission regulation. Firstly,a numerical simulation model of the after-treatment system was established using computational fluid dynamics（CFD）,and the physicochemical processes was optimized and parameterized by NH₃ distribution uniformity test. Then,based on the simulation and test results,the broken grille,diversion device and micro-hole board were designed for better mixing and NH₃ distribution uniformity. Simulation results show that under high temperature and high speed conditions,the velocity distribution uniformity in SCR₁ is improved from 0.951 to 0.976,and the NH₃ distribution uniformity is improved from 0.947 to 0.979 with a negligible increase of pressure loss. High mixing performance and excellent anti-deposition capability can be also shown from the transient urea deposition test results.