Abstract: The requirements for miniaturization and integration of new detection devices as well as the demands for interdisciplinary manipulation platform by current scientific researches and engineering applications prompt the rapid development of microfluidics. Droplet and particle are two important targets that are manipulated by microfluidics, which usually works at the laminar flow domain. Nonlinear factors are introduced into microscale flow by scale effect and interface effect, which are influenced by multiple parameters including the channel geometry and flow condition. In order to understand the complex flow phenomena, physical mechanisms should be studied from the fundamental perspective of hydrodynamics. Related work of our group on behaviors of droplets and particles over recent years is summarized. By analyzing the variation of characteristic parameters of droplet or particle, distinct flow regimes and corresponding critical conditions can be specified. Key control parameters dominating the flow can be confirmed and theoretical models can be constructed to pursue the manipulation methods of different behaviors. This study can provide references for the improvement of the theoretical system of complex flow at microscale and the related engineering applications.