The nonlinear natural thermal vibration of a rectangular orthotropic plate on a nonlinear foundation was studied. To get a highaccuracy approximate solution which can't be obtained with the normal LP method, the strongly nonlinear vibration system of the nonlinear natural thermal vibration of the rectangular orthotropic plate on the nonlinear foundation was changed to a weakly nonlinear vibration system firstly by the parameter transformation, and then the highaccuracy approximate solution can be obtained with the improved LP method. The effects of temperature, characteristic parameter of foundation, ratio of length and width etc. on the natural thermal vibration frequency were discussed. The results showed that the natural thermal vibration frequency decreased with the increase of temperature and increased with the increase of the characteristic parameter of foundation and ratio of length and width.