By using the characteristic of pair production of D mesons at center-of-mass en- ergy of 3. 773 GeV, we developed a method to calibrate the center-of-mass energy of BEPC-Ⅱ by reconstructing single tag D meson. This method can be used to precisely calibrate the center-of-mass energy of BEPC-Ⅱ offline when BESIII d...