In　this　paper,　we　study　the　spreading　of　infections　on　complex　heterogeneous　networks　based　on　an　SEIRS　epidemic　model　with　nonlinear　infectivity.　By　mathematical　analysis,　the　basic　reproduction　number　R-0　is　obtained.　When　R-0　is　less　than　one,　the　disease-free　equilibrium　is　globally　asymptotically　stable　and　the　disease　dies　out,　while　R-0　is　greater　than　one,　the　disease-free　equilibrium　becomes　unstable　and　the　disease　is　permanent,　and　in　the　meantime　there　exists　a　unique　endemic　equilibrium　which　is　globally　attractive　under　certain　conditions.　Finally,　the　effects　of　various　immunization　schemes　are　studied.　To　verify　our　theoretical　results,　the　corresponding　numerical　simulations　are　also　included.