Transport properties in a nanoparticle-laden flow are of great importance for their practical use, such as in tubular reactor-based photocatalytic technologies. In our study, an experimental setup based on photocatalytic application was employed to investigate the nanoparticle transport characteristics in a flow reactor. An interesting periodical attenuated oscillation of the particle volume fraction and mean particle size with time was found in the nanoparticle-laden flow. We further analyzed the period of the attenuated oscillation curve by conducting a linear fitting, which shows that the period can be expressed as T = f(Q,L) in which the period is proportional to the length of the test section and inversely proportional to the flow rate. We found that the time 5T is a very important criterion for determining whether the particle suspension has reached the quasi-steady state and whether the nanoparticle has been well suspended. Our work is believed to be valuable, efficient, and effective in the study of transportation of nanoparticles in laminar flow with low energy consumption.