Abstract: Functionally graded material (FGM) disk subjected to thermal load was investigated based on thermally coupled theory. According to the theory of FGM construction and the axisymmetric characteristic of the disk, the full field distribution of its mechanical properties was obtained. The temperature distribution of the disk was deduced and analyzed by the functionally constructed method and the thermally coupled conduction equation, respectively. Thermally coupled constitutive relations combined with the temperature distribution were established, and their material constants were determined due to the principle of mechanical properties of thermoelastic materials under the two dimensional condition. The displacement governing equations of different FGM structural form disk in different temperature distribution were solved using the differential quadrature method(DQM). The results reveal that thermally coupled constitutive relations can be degenerated to Hooke's laws at room temperature. The error of radial displacement of the disk under classical thermoelastic theory and thermally coupled theory can reach 41.7%. The results of thermally coupled theory change with temperature nonlinearly, and this change trend is also reflected in a large number of scientific experiments. The thermoelastic field in a disk is significantly influenced by temperature change of the outer surface in a disk, angular speed, and temperature distribution.