Diesel engine has many advantages such as high thermal efficiency, low fuel consumption and the low emission of CO2. However, diesel engine is not able to avoid the emission of NOx and PM. To suppress the engine out emission in terms of NOx, LNT(Lean NOx Trap) and SCR(Selective Catalytic Reduction) are considered as a good solution to cope with severe emission regulation. De-NOx systems need a dosing unit to supply reducing agent. Thus, the spray characteristics are important factors for NOx conversion efficiency. In this paper, the characteristics of an injector used for HC De-NOx system are investigated before and after an endurance test. The spray images were taken with a high speed camera, and the spatial distribution of the spray was analyzed using image processing technique.