The invention belongs to the technical field of organic chemical synthesis, and relates to a synthetic method of triphenylene, in particular to a synthetic method of 2,7-dibromo-benzo[9,10]phenanthrene. The synthetic method includes dissolving 4,4'-dibromobiphenyl in dichloromethane; adopting a mixed solution of nitric acid and sulfuric acid for nitration reaction, and carrying out washing, concentrating and recrystallizing to obtain 2-nitro-4,4'-dibromobiphenyl, wherein the yield is 82%; reducing a nitro group into an amino group by a Fe/NH4Cl system, and subjecting the obtained product and benzene to diazo coupling reaction to obtain 4,4'-dibromo-1,1',2',1-terphenyl; performing oxidative coupling by a Pd/trifluoromethanesulfonic acid system to obtain the 2,7-dibromo-benzo[9,10]phenanthrene, wherein the yield is 62.5%, and the HPCL purity is 99.5%. The synthetic method avoids the problems of complex synthesis, low yield and environmental pollution in conventional methods.