The mean residence time of a material in the system containing an eddy was calculated with the experimental results. The relation between the system mean time which was obtained by the first moment of the stimulus-response curve and the mean residence time which was the ratio of the system volume to the fluid flow rate was investigated. If there was no eddy in the system, the system mean time equaled to the mean residence time. For the system containing an eddy, the system mean time was greater than the mean residence time. And the numerical value of the discrepancy between them increased with the aspect ratio, AR and inversely with the Reynolds number.