Micro－zone morphologic and phase changes of TATB/AU films were studied with in－situ AFM on a thermal stage in long－duration. The fixed－frequency of selected probe, DFM20N, was 0.38 N·m^－1,and the scan module was Tapping Mode. The other parameters were 75 ℃ stage and 0.15 fps for sampling images. Nonlinear expansion was observed in this experiment. Depolymerization and reaggregation of polyester type of urethane (AU) coating TATB were presumed by analyzing images. The coated TATB grain doe not change its shape before 15 h, but it is split quickly after 19 h. The results show that the cut－throat shape variation of adhesive (AU) accelerates the cleavage of TATB crystal fine grains.