The microstructure and surface morphology evolution of degummed Bombyx mori silk were investigated by X-ray diffraction,FT-IR microscope and polarization microscope over a broad temperature range from 30 ℃ to 300 ℃.The results indicate that the thermal expansion coefficients of lattice are highly anisotropic along a and b axial during heating.The thermal expansion coefficient along a axial is much smaller than that along b axial because of strong hydrogen bonding force along a axial.Besides,the crystallinity of baves begins to increase from 180 ℃ for the transition from the random coil to β-sheet,and decrease significantly at 280 ℃ when the carbonization occurs.It is also found that the degree of orientation increases slightly during the entire heating process.