This article studies the existion of homoclinic orbit bifurcation of sirs modle , moreover , it determines the relative location of stable manifolds and unstable manifold of hyperbolic fixed points of this system , therefore , it shows the parameter range of existing limit circle 本文討論了具有暫時免疫傳染病模型同宿軌道分支的存在性,利用melnikov函數(shù)確定了該系統(tǒng)雙曲不動點的穩(wěn)定和不穩(wěn)定流形的相對位置,從而給出存在極限環(huán)的參數(shù)范圍。