The phase transformation in calcification process was investigated by X-ray diffraction(XRD) and differential scanning calorimeter(DSC), and the effect of calcification on the leaching rate of rare earth was analyzed. The results show that bastnaesite transforms into rare earth hydrate at the calcification temperature range of 225–300 °C. However, this transition is verified to be an efficient reaction for the activating bastnaesite when the temperature is higher than 200 °C. The leaching rate of rare earth increases to 89.17 %for activating bastnaesite from 36.27 % for the bastnaesite,and it is the highest with calcification temperature of 250 °C,which is consistent with the result of DSC analysis. The transition of rare earth oxyfluoride into RE(OH)_3 is accelerated by the addition of NaOH according to the experiments of different calcification systems. The phase transformation in calcification process was investigated by X-ray diffraction (XRD) and differential scanning calorimeter (DSC), and the effect of calcification on the leaching rate of rare earth was analyzed. The results show that bastnaesite transforms into rare earth hydrate at the calcification temperature range of 225-300 ° C. However, this transition is verified to be an efficient reaction for the activating bastnaesite when the temperature is higher than 200 ° C. The leaching rate of rare earth increases to 89.17% for activating bastnaesite from 36.27% for the bastnaesite, and it is the highest with calcification temperature of 250 ° C, which is consistent with the result of DSC analysis. The transition of rare earth oxyfluoride into RE (OH) _3 is accelerated by the addition of NaOH according to the experiments of different calcification systems.