Inflammatory stress is closely related to metabolic disease and insulin resistance. The precise cellular mechanism linking obesity and diabetes is largely unknown, but about 14–20% of obese individuals develop diabetes. In this study, we investigated whether chronic inflammation exacerbated glucose metabolism disorder by impairing β cell function in high-fat diet (HFD)-fed C57BL/6J mice. We used sc casein injection to induce chronic inflammation in HFD-fed C57BL/6J mice; 14 weeks on a HFD resulted in weight gain, hyperlipidemia, and low insulin sensitivity in these mice which nevertheless had normal blood glucose and serum inflammatory cytokines levels. Casein injection in the background of HFD elevated serum tumor necrosis factor α (TNFα) and serum amyloid A levels and increased TNFα and MCP1 expression in the adipose tissue, liver, and muscle of HFD-fed mice. Chronic inflammation induced by casein injection further decreased insulin sensitivity and insulin signaling, resulting in insulin deficiency and hyperglycemia in these mice. Islet mass and insulin content were markedly increased in HFD mice. However, in contrast with HFD-fed alone, chronic inflammation in HFD-fed mice decreased both islet mass and insulin content, reduced the genetic expression of insulin synthesis and secretion, and increased β cell apoptosis. We conclude that chronic inflammation exacerbated glucose metabolism disorders by impairing β cell function in HFD-fed C57BL/6J mice, suggesting that this mechanism may operate in obese individuals with chronic inflammation, making them prone to hyperglycemia.