Abstract: A thermal modal analysis method was established by considering the effects of material property's change, thermal stress and deformation to investigate thermal modal evolution of composite stiffened and connecting plates. The calculation results show that material property's change and thermal stress result in the increasing in modal frequencies under thermal buckling temperature. In post-buckling stage, the nonlinear deformation can increase the stiffness of panel structures, which makes the modal frequencies increase. Mode changes occur during the whole warming-up process and modals tend to be dense; Initial deflections, size of stiffeners and reinforcement patterns have great influence on the critical buckling temperature of stiffened plates. Mode shapes are also changed and appear characteristics of localized. For connecting plates, due to the similarity of thermal deformation and modal shape, the modal frequency will jump from the lower order to the higher.