In this paper, boron and nitrogen co-doped diamond was synthesized under the condition of 5.5 GPa and 1 300 ℃ by temperature gradient growth method. Then the synthetic diamond was annealed under the pressure of 5.0 GPa and the temperature of 2 000 ℃ and 2 100 ℃. FT-IR spectra demonstrate that the singly substituted form nitrogen (C-center) in the crystal after high pressure and high temperature (HPHT) annealing is transformed into the aggregation form nitrogen (A-center), and the concentration of A-center nitrogen increases with the annealing temperature. The concentration of positively charged nitrogen ion (N+) in the crystal is not affected by HPHT annealing treatment. After high temperature annealing, NV0 and NV- center appear in the diamond, but disappear when the annealing temperature continues to increase. HPHT annealing has no obvious effect on the structure and internal stress of diamond crystal. After HPHT annealing treatment, the thermal stability of diamond is improved, the initial oxidation temperature, intense oxidation temperature and the temperature point where the mass sharply decrease are increased by 65 ℃, 55 ℃ and 61 ℃, respectively. This paper provides guidance for the HPHT annealing treatment application to boron and nitrogen co-doped diamond.