The invention relates to the technical field of aromatic hydrocarbon preparation, in particular to a composite catalyst, a preparation method and application thereof, and a method for preparing aromatic hydrocarbon from synthesis gas through a one-step method. The mass ratio of the metal oxide to the molecular sieve is (1-5): 1, the molecular formula of the metal oxide is MnxZnyCrzAl0. 1O4, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt, 0 lt and 0 lt; xlt; 1, 0lt; yt; Yt; 1.6, 1lt; zlt, zlt; (x + y) / z is equal to 0.3-1.5, and the molecular sieve is an HZSM-5 molecular sieve. When the composite catalyst provided by the invention is used for preparing aromatic hydrocarbon from synthesis gas by a one-step method, the CO conversion rate is greater than or equal to 19%, the aromatic hydrocarbon selectivity is greater than or equal to 75.8%, and the space-time yield of aromatic hydrocarbon is greater than or equal to 0.07 g / h.gcat; meanwhile, the composite catalyst provided by the invention has relatively high stability and long service life, and no obvious inactivation phenomenon exists when the composite catalyst stably runs for 100 hours.