High-nitrogen energetic compound 3,6-diamino-1,2,4,5- tetrazine-1,4-dioxide (DATZO₂) was synthesized from 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2-dihydro-1,2,4,5- tetrazine (BDT) by a two-step reaction sequence, with an overall yield of 46.8% at the 30 g scale. 3,6-bis(3,5-dimethylpyrazol-1-yl)-1,2,4,5- tetrazine (BT), which is an important synthesis intermediate, was obtained by using oxygen as oxidizer without N_xO_y. A series of synthesis and recrystallization methods was developed to yield different particle sizes and morphologies, and their sensitivity were tested. The thermal decomposition of DATZO₂ was investigated, kinetic parametes of decomposition and mechanism functions were obtained.