To understand MHD behavior of flow in a conductivity rectangular duct with flow channel insert (FCI), the more experiments of MHD flow in 304 stainless steel (SS) duct with 304 FCI are carried out after gotting the primary experimental results of the duct with epoxy FCI. The new experimental results indicate that the velocity distribution in the cross section of the duct with 304 SS FCIs  cases is significantly different from that with epoxy FCIs cases, and that MHD pressure drop in 304 FCI PES case is lower than that in epoxy FCI  PES case. These experimental results cannot be explained by the current MHD theory and modeling. So, we try to understand the velocity distribution and MHD pressure drop by analyzing the experimental data of the electric potential difference between FCI box walls and 304 SS duct walls and using the secondary flow MHD effect. An MHD pressure drop FCI electric conductivity correction factor is addressed and took together with previous geometry sensitivity correction factors can well explain the MHD pressure drop experimental results.