System-level models containing engine model, emission models, and aftertreatment device models have been developed. All the sub-models have been developed separately and come from a variety of different sources. A new phenomenological CO model recently has been coupled into the previous integrated model. The emission models, including PM (particulate matter), NOx, and CO are also calibrated from experimental data. Some modification has been added to improve the integrated model and accept different aftertreatment device models for future work. The objective of this work is to study the DPF (Diesel Particulate Filter) regeneration during transient operating conditions using the integrated model.The integrated system-level model is used to studying the dynamic performance between engine and aftertreatment system. In this study, the calibrated emission models are validated at transient operating conditions. Passive and active DPF regenerations are also conducted for load and speed transients to study the transient effects on regeneration. The effects of exhaust mass flow rate, and temperature on pressure drop across the DPF during regeneration are investigated.