2,4,6-trinitroaniline (TNA) was synthesized by trinitro-chlorobenzene and aqueous ammonia in alcohol, and then reacted with 4-amino-1,2,4-triazole (ATA) to generate 1,3,5-triamino-2,4,6-trinitrobenzene (TATB) by VNS（Vicarious nucleophilic substitution） reaction with total yield of 95.7％.The structures of TNA and TATB were characterized by FTIR, NMR, MS and elementary analysis. Effects of CH₃ONa， ATA and the reaction time were investigated on the overall yield of TATB. The optimized conditions of VNS reaction were： the mass ratio of TNA, ATA and NaOCH₃ is 1：6：14, reaction temperature is 70 ℃, and time is 2 hours. The ultra fine TATB with average particle diameter D₅₀ of 0.151 μm was obtained using aqueous mineral acid solutions to quench the reaction. The particle-size and crystal were analyzed.