Formation of droplets especially in microchannels, micro-electro-mechanical systems (MEMS) and polymer electrolyte membrane fuel cells and their effects on the performance of these devises, as well as scientific aspect of the droplet behavior in the fluid flow motion, makes the subject of the droplet deformation and motion an attractive problem. In this work, we numerically simulate the deformation of a drop of water attached to the wall of a channel flow using full two-dimensional Navier–Stokes equation and the volume-of-fluid method for capturing the interface. The effects of channel inlet velocity, the density and viscosity of the surrounding fluid, and the surface tension coefficient on the flow structures both inside and outside of the droplet as well as the deformation of the droplets are examined. Several test cases, which cover rather wide range of the Reynolds and capillary numbers, based on the surrounding fluid properties and the diameter of the droplet are performed. The Reynolds number, Re, range is from 24 to 1800 and the capillary number, Ca, is from 0.014 to 0.219. It is found that the droplet shape changes and depending on the capillary and Reynolds numbers, it eventually reaches an equilibrium state when there is balance between the surface tension, inertia, and the viscous forces. It is also found that the deformation of the droplet does not depend on the capillary numbers, when Ca is small, but it is a strong function of Ca, when it is large.