We　present　a　thermal　model　to　describe　the　interaction　between　the　visible　modes　in　micro-ring　resonators　from　the　third　harmonic　generation　(THG)　nonlinear　process.　We　demonstrate　that　the　model　can　predict　the　thermal　characteristics　of　the　orthogonal　THG　modes　from　the　interaction　and　of　the　resonance　coupling　between　them　in　micro-ring　resonators　having　a　strong　nonlinear　thermo-optic　coefficient.　Furthermore,　the　model　can　be　used　to　extract　the　THG　efficiency,　the　linear　and　nonlinear　thermo-optic　coefficients　and　the　polarization　dependency　of　the　THG　modes　from　the　measurement　data.