Calcium silicate hydrate (C-S-H) with Ca/Si ratio 1.0 was prepared via precipitation in solution and heated at various temperatures to investigate its dehydration behavior. The dehydration, structural collapse and recrystallization characteristics of C-S-H and its microstructural change during heating process were investigated by XRD, SEM, Raman and TG-DSC techniques. C-S-H gradually lost non-evaporable water upon heating, about 50％ and 80％ non-evaporable water was removed below 200 and 400 ℃, respectively, and the rest was removed up to about 1000 ℃. At 400 ℃, dehydrated C-S-H exhibited the increasing disordering of calcium/silicon environment and the decreasing symmetrical bending vibration of Si-O-Si of Q2 silicate chains. At 650 ℃ non-bridging oxygen atoms (Onon) attached to silicon were almost removed, and significant structural change occurred, and at 815 ℃ C-S-H dehydrated to wollastonite.