Type 2 diabetes (T2D) is a metabolic disorder with high prevalence and severe complications that has recently been indicated to be treatable by a combined static magnetic field (SMF) and electric field. We systematically compared four types of SMFs and found that a downward SMF of ∼100 mT could effectively reduce the development of hyperglycemia, fatty liver, weight gain, and tissue injury in high-fat-diet (HFD)/streptozocin-induced T2D mice, but not the upward SMF. The downward SMF markedly restored the Bacteroidetes population and reversed the iron complex outer membrane receptor gene reduction in the mice gut microbiota, and reduced iron deposition in the pancreas. SMF also reduced the labile iron and reactive oxygen species level in pancreatic Min6 cells in vitro and prevented palmitate-induced Min6 cell number reduction. Therefore, this simple SMF setting could partially prevent HFD-induced T2D development and ameliorate related symptoms, which could provide a low-cost and non-invasive physical method to prevent and/or treat T2D in the future.