The invention belongs to the technical field of aromatization industrialization devices and methods, and in particular relates to an on-line sampling system and method for an aromatization process. The on-line sampling system disclosed by the invention consists of an introduction device, a gas-solid separation device, a cooling device, a gas-liquid separation device, a gas-phase product dewatering and drying device, a gas-phase metering device, a gas-phase sampling device, a liquid-phase sampling device and a tail gas absorption device. The method comprises the following steps of introducing a preheated material into the on-line sampling system, removing a catalyst through the gas-solid separation device, cooling the material through the product cooling device, performing phase division through the gas-liquid separation device, enabling a gas-phase product to flow out from the top, performing dewatering and drying, and metering and collecting a gas sample for analysis; and collecting a liquid-phase product at the bottom of the gas-liquid separation device so as to perform liquid division weighing. The method disclosed by the invention can precisely quantify gas phase, oil phase and water phase of an aromatization system product, so that the environment friendliness and the safety of the sampling device are fully considered; the on-line sampling system is simple in structure, convenient to use and extremely high in operability.