This paper introduces the design and characterization of a flow tube reactor (Jiao-FTR, termed as J-FTR) for the study of aerosol formation mechanism. The flow field, the injection effect of the movable inlet, as well as the average residence time of gases and particles in the J-FTR under different configurations and operating conditions were characterized using a combination of computational fluid dynamics (CFD) simulations and direct measurements. The results show that the way of flow addition in the premixing section, the main flow rate, and the movable inlet geometry significantly affect the flow field and the residence time of gases and particles in the J-FTR. The premixing section aids in the development of a laminar main flow in the reactor. When the main flow was smaller than 8L/min, the flow became laminar before it entered the main reaction section of the reactor. When the movable inlet employed a straight tube with a relatively larger inner diameter or a cross-tube, its injection effects can be largely reduced or avoided. These results not only provide important guidance for performing J-FTR experiments of VOCs oxidation and aerosol formation, but also provide reference for other researchers to design FTR and carry out flow tube experiment.