Emission control technologies are required to achieve stringent emission regulations such as Beijing 6 (equivalent to Europe 6). In order to meet Europe 6 emission regulation, diesel oxidation catalyst (DOC) upstream of catalyzed diesel particulate filter (CDPF) with supplementary fuel injection (hydrocarbon injection (HCI)) are used for the X7 diesel engine to control the particulate matter (PM) for a heavy-duty diesel engine. This study investigated soot loading and active regeneration process in a CDPF by using secondary fuel injection in order to enhance exothermal heat which is needed to raise the CDPF temperature. The injected fuel is burnt in a DOC where the injector is mounted in the tailpipe upstream of DOC. In order to control the regeneration process of CDPF, several issues should be considered in the study: the amount of diesel injected into the aftertreatment system; the injector location and orientation; hydrocarbon (HC) concentration field on the DOC upstream; temperature and pressure distribution at CDPF. For this purpose, a numerical combination of the aftertreatment technology DOC-CDPF model has been established by using commercial computational fluid dynamics (CFD) code. The aftertreatment model is validated by comparing the simulation results with the measured data and good agreement was observed.