Abstract: The effect of iron content on the kinetics of talc dehydration was studied with talc of different iron values using in-situ synchrotron X-ray diffraction (XRD).The sample particle size is 2~5μm.The air atmosphere synchrotron radiation in situ XRD de-hydration experiment was carried out under atmospheric pressure.High content of iron obviously resulted in lower dehydration tem-perature.The difference of the dehydration temperature of two samples was above 127℃.The dehydration of talc followed random nucleation and growth mechanism, and fitted Avrami equation, with n being 1.669.The results suggest that the dehydration of differ-ent iron values of talc may occur at the different depths around hundreds of kilometers, so the study was significant to the understand-ing of the genetic mechanism of earthquakes in the subduction zone.