We produced cadmium sulfide (CdS) nanoparticles in the continuous flow microreactor via precipitated reaction in aqueous solutions, and analyzed the nanoparticle size at different flow rates by using an in-situ spectroscopy technique. Applying deconvolution fitting method, this result shows the size increases from 1.13 nm to 1.26 nm for the corresponding residence time from 0.26 to 3.96 s. According to the growth curve of CdS nanoparticle, we propose the barrier controlled coalescence mechanism as a reasonable model to describe the CdS nanoparticle growth in the continuous flow microreactor. Also, applying computational fluid dynamics, low skewness value (s = 0.09) of the RTD curve at high flow rate (17 mL/min) suggests good radial mixing in the corresponded short residence time. (C) 2018 Elsevier B.V. All rights reserved.