It has been observed that a certain percentage of diesel particulate filters (DPFs) from the field form mid-channel ash plugs both in light duty and heavy duty applications. As revealed in a post mortem study, some field samples have ash plugs of 3-10 cm length in the middle of DPF inlet channels, which can potentially reduce the inlet channel volume by more than 50%. As a result, the mid-channel ash plug reduces the effective filtration area and decreases the effective channel open width in the middle of the channel. This explains why these filters are reported as having large increases in pressure drop. Moreover, the mid-channel ash deposits reduce the DPF service life and render the filter cleaning process ineffective.In the present study, an open source CFD tool is applied to study the 3D flow crossing two representative inlet and outlet DPF channels where the inlet channels have mid-channel ash plugs. A systematic grid convergence study is conducted to ensure that the CFD results are grid independent. A heavy duty DPF is investigated and the mid-channel ash plug is assumed to be 6.8 cm long. Several cases ranging from 50% to 80% channel open width reduction are discussed. The simulations show that mid-channel plug can increase the DPF pressure by 30% to 80%. Meanwhile, the mid-channel deposits change the pressure and wall velocity distribution along the DPF length direction. In addition, an algorithm is introduced to calculate the entire DPF pressure drop when it has multiple types of mid-channel plugs. This paper presents a theoretical means to predict mid-channel ash plug effects on DPF pressure drop.