The hydrogen internal combustion engine has the characteristics of zero carbon emission and is an important method to achieve low cost carbon neutrality. However, the high temperature environment of incylinder combustion will generate a large amount of nitrogen oxide(NO_x) emissions. The use of selective catalytic reductio(SCR) reducing NO_x technology is a necessary method to expand its large scale application and continue improving power and economy performance. The experiment verified that the NH₃-SCR aftertreatment system of Cubased molecular sieve was an efficient NO_x purification scheme for direct injection hydrogen engine. A simplified reaction mechanism was used to model and simulate the NH₃-SCR reaction process, and the effects of reaction temperature, space velocity and NH3nitrogen ratio on NO_x reduction by NH₃-SCR were studied under the boundary of hydrogen internal combustion engine. The results show that the lowtemperature activity of ammonia SCR is still good under the boundary of lean burn hydrogen combustion engine with direct injection. The ignition temperature(T₅₀) of aftertreatment system is 110 ℃, and the activity window(T₉₀) ranges from 150 ℃ to 425 ℃. When the airspeed is greater than 25 000 h^－1, the NO_x conversion efficiency remains greater than 95%. When the ammonia nitrogen ratio is 0.5 and the reaction temperature maintains at 350-400 ℃, the highest NO_x conversion efficiency can be guaranteed and the nearzero NO_x emission of direct injection hydrogen combustion engine can be achieved.