This　paper　investigates　the　nonlinear　breathing　vibrations　and　chaos　of　a　circular　truss　antenna　under　changing　thermal　environment　with　1:2　internal　resonance　for　the　first　time.　A　continuum　circular　cylindrical　shell　clamped　by　one　beam　along　its　axial　direction　on　one　side　is　proposed　to　replace　the　circular　truss　antenna　composed　of　the　repetitive　beam-like　lattice　by　the　principle　of　equivalent　effect.　The　effective　stiffness　coefficients　of　the　equivalent　circular　cylindrical　shell　are　obtained.　Based　on　the　first-order　shear　deformation　shell　theory　and　the　Hamilton＇s　principle,　the　nonlinear　governing　equations　of　motion　are　derived　for　the　equivalent　circular　cylindrical　shell.　The　Galerkin　approach　is　utilized　to　discretize　the　nonlinear　partial　governing　differential　equation　of　motion　to　the　ordinary　differential　equation　for　the　equivalent　circular　cylindrical　shell.　The　case　of　the　1:2　internal　resonance,　primary　parametric　resonance　and　1/2　subharmonic　resonance　is　taken　into　account.　The　method　of　multiple　scales　is　used　to　obtain　the　four-dimensional　averaged　equation.　The　frequency-response　curves　and　force-response　curves　are　obtained　when　considering　the　strongly　coupled　of　two　modes.　The　numerical　results　indicate　that　there　are　the　hardening　type　and　softening　type　nonlinearities　for　the　circular　truss　antenna.　Numerical　simulation　is　used　to　investigate　the　influences　of　the　thermal　excitation　on　the　nonlinear　breathing　vibrations　of　the　circular　truss　antenna.　It　is　demonstrated　from　the　numerical　results　that　there　exist　the　bifurcation　and　chaotic　motions　of　the　circular　truss　antenna.