The multiferric BiFeO3 (BFO) has attracted much attention due to its magnetoelectric coupling effects. However, the phase transformation involved in the reaction sintering is still not clarified, which consequently restricts the synthesis of pure-phase BiFeO3 ceramics. In-situ High Temperature Raman Spectroscopy (in-situ HT-Raman)is a powerful means to characterize complex solid phase transitions and reactions. In this paper, the phase transformation in the reaction sintering of BiFeO3 ceramics with different molar ratio (1∶1, 1.03∶1 or 1.05∶1) of Bi2O3-Fe2O3 and heating/cooling rates (10, 100 ℃·min-1) was studied by In-situ HT-Raman for the first time. We also studied the thermal contraction of the sintering product in cooling process. Results showed that two intermediate transition phases Bi2Fe4O9 and Bi25FeO39 will be produced in the reaction sintering process of BFO ceramics. The content of impurity phases mainly depends on the molar ratio of Bi2O3-Fe2O3 and heating/cooling rates, and 1.03∶1 with higher rate is optimum. There is a good linear relation ship between BFO A1-1 peak position and temperature in the cooling process, which indicates that the temperature reduction only brings about the lattice contraction of BFO ceramic and no structural change. Moreover, the phase composition and morphologies of sintering products were measured by Two Dimensional X-ray Diffraction (2D-XRD) and Electron Backscattered Diffraction (EBSD). XRD results showed that the content of impurity phases is relatively low when Bi is excessive, which is consistent with Raman results. Combined 2D-XRD and EBSD results, rapid heating/cooling rate is beneficial to the grains nucleation and growth, on account of the larger and more uniform grains when Bi exceeds 3%. This work provides useful experimental guidance for the preparation of pure-phase BiFeO3 ceramics by further elucidating its mechanism of phase transformation in the reaction sintering.