An　epidemic　model　with　stage　structure　is　formulated.　The　period　of　infection　is　partitioned　into　the　early　and　later　stages　according　to　the　developing　process　of　infection,　and　the　infectious　individuals　in　the　different　stages　have　the　different　ability　of　transmitting　disease.　The　constant　recruitment　rate　and　exponential　natural　death,　as　well　as　the　disease-related　death,　are　incorporated　into　the　model.　The　basic　reproduction　number　of　this　model　is　determined　by　the　method　of　next　generation　matrix.　The　global　stability　of　the　disease-free　equilibrium　and　the　local　stability　of　the　endemic　equilibrium　are　obtained;　the　global　stability　of　the　endemic　equilibrium　is　got　under　the　case　that　the　infection　is　not　fatal.　(C)　2007　Elsevier　Ltd.　All　rights　reserved.