Geometry sensitivity of magnetohydrodynamics (MHD) duct flow and some ab-normal phenomena deviating from the classical MHD laws were measured in an experimentalinvestigation of the MHD effect of the flow channel inserter (FCI) duct flow. The results showedthat the velocity distribution deviated from the M-type profile on the centre-plane of the crosssection of the duct with small slots (in short “S-duct”). The electric potential difference in theduct wall was much lower than that given by the classical electromagnetic laws. The MHD pres-sure drop was much higher than that from the classical magneto-hydrodynamics theory. Theseresults may help us find some new methods to reduce the MHD pressure drop, or explore otherpotential applications such as flow structure control. Geometry sensitivity of magnetohydrodynamics (MHD) duct flow and some ab-normal phenomena deviating from the classical MHD laws were measured in an experimental investigation of the MHD effect of the flow channel inserter (FCI) duct flow. The results showed that the velocity distribution deviated from the M-type profile on the center-plane of the crosssection of the duct with small slots (in short “S-duct”). The electric potential difference in theduct wall was much lower than that given by the classical electromagnetic laws. The MHD pres-sure drop was much higher than that from the classical magneto-hydrodynamics theory. These results may help us find some new methods to reduce the MHD pressure drop, or explore other potential applications like flow structure control.