A single inlet and multi-inlet hollow fiber modules (HFMs) were designed in order to investigate the fluid hydrodynamics of the shell side. Residence time distribution (RTD) curves was measured under different packing density and inlet. Mean residence time ( ), variance( ) and the number of tanks (N) were also calculated to reflect the degree of backmixing. The experimental results indicated that the random packing of fiber caused the non-ideal flow in shell side. With the increasing of the packing density, the non-ideal flow was more serious. Contrasting to the traditional one, multi-inlet hollow fiber modules could weaken the trailing of the RTD curves and control the backmixing. With the quantity and the site of the inlets changed, non-ideal flow can be further improved. The hydraulic characterization of the shell side flow were related with not only the quantity but also the site of inlets. The results indicated that the muti-inlets design is superior to that of a single inlet.