The fuel injection assisted combustion characteristics test of diesel oxidation catalyst was conducted on the engine bench. The DOC temperature rise and aftertreatment emission performance were analyzed through the fuel injection in tail pipe. The result shows that the temperature of DOC increases rapidly within 100 seconds through the fuel injection, the temperature rise decreases with the increase of rotational speed and becomes faster with the higher temperature of incoming flow and the higher speed. In order to keep a high enough temperature before DPF, it is necessary to control the exhaust temperature, air velocity and injection pulse width reasonably. THC concentration is near to zero before diesel injection and sharply increases at the moment of injection. Accordingly, high exhaust temperature, low air velocity and small injection volume are conducive to THC leakage control. Besides, diesel injection can reduce NO₂ production.