Next-generation vehicles which include Electric Vehicles, Hybrid Electric Vehicles and Plug-in Hybrid Electric Vehicles are researched and expected to reduce CO2 emission in the future. In order to reduce the emissions of the heavy-duty diesel plug-in hybrid vehicles (PHEV), it is necessary to provide the high exhaust-gas temperature and to keep the aftertreatment system effective. The engine starting condition of PHEV is cold, and the engine start and stop is repeated. And, the engine load of the PHEV is assisted by the electric motor. Therefore, the aftertreatment system of PHEV is not able to get the enough high exhaust-gas temperature. And, the warm-up of the exhaust-gas aftertreatment system for PHEV is spent the long time. So, it is worried about a bad effect on the emission characteristics of PHEV. In this study, we focused on the electrical heating catalyst system (EHC), which is one of the next generation electrical technologies. This test PHEV was equipped with EHC. The fuel economy and emission characteristics of this test PHEV were estimated using the extended-HILS, which is combinate the real engine with the PHEV model of the HILS (Hardware-In-the-Loop-Simulator). This result is that the EHC showed good performance at the engine low speed and low torque range. And, NOx emission was reduced when the tailpipe layout was setup in order of the urea solution injector, EHC and SCR catalyst. NOx and CO2 emission of this test PHEV which was equipped with EHC was good, compared with the heavy-duty diesel vehicle, the heavy-duty diesel hybrid vehicle and conventional PHEV which was not equipped with EHC.