The invention discloses an in-situ synthesis method of a catalyst for preparing aromatic hydrocarbon employing methanol/dimethyl ether conversion. The method comprises the following steps: firstly, preparing mixed slurry from a silicon source, an aluminum source and water, and preparing microspheres granules containing silicon-aluminum oxide through a spray drying process; roasting the microspheres granules containing the silicon-aluminum oxide to obtain a microsphere catalyst carrier; preparing a mixed solution from the microsphere catalyst carrier, a templating agent, a first metal component precursor, a phosphorus modifier, an acid-alkali regulator and water, enclosing into a stainless steel synthesis reactor, heating to carry out constant-temperature crystallization, and separating a solid product; washing the solid product with deionized water until being neutral, and drying and roasting to obtain a microsphere catalyst containing a ZSM-5 molecular sieve; and finally, dipping the microsphere catalyst into a second metal component precursor solution, and drying and roasting to obtain the microsphere catalyst for preparing the aromatic hydrocarbon employing methanol/dimethyl ether conversion. According to the in-situ synthesis method, catalyst deactivation caused by bonding of metal components in the catalyst and a binder can be effectively blocked.