The invention relates to an SAPO-34/ZSM-5 composite molecular sieve and a synthesis method of the composite molecular sieve, solving the problems of single pore diameter, low acidity and low reaction activity of the porous materials which are synthesized by the prior art. The synthesis method of the composite molecular sieve comprises the following steps: firstly mixing a silicon source, an aluminum source, a phosphorus source and an organic template agent according to a certain ratio, then adding a certain quantity of ZSM-5 molecular sieves, uniformly mixing and carrying out hydrothermal crystallization, and synthesizing the SAPO-34/ZSM-5 composite molecular sieve by controlling nucleation and crystal growth conditions, wherein the composite molecular size is adjustable in ratio of two phases; an XRD diffraction spectrum of the composite molecular size has a maximum d interval at the positions of 7.92+/-0.1, 8.79+/-0.1, 9.52+/-0.1, 12.85+/-0.1, 16.00+/-0.1, 20.56+/-0.1, 23.01+/-0.05, 23.24+/-0.05, 23.86+/-0.05, 25.83+/-0.1, 30.55+/-0.1 and 31.32+/-0.1. The composite molecular sieve can be applied to industrial production for preparing aromatic hydrocarbon by reacting methyl alcohol/dimethyl ether.