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(shí)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(dòng)點(diǎn)的穩(wěn)定和不穩(wěn)定流形的相對(duì)位置,從而給出存在極限環(huán)的參數(shù)范圍。