The flows in micro scale present some new phenomena different from those in macro scale,which introduce new questions in fluid mechanics.In this talk,some questions related with the microchips design will be discussed:1 Resistance forces.In microchannel designs,the driven pressures or electrical potentials are depended on flow-rates or geometrical sizes theoretically.But when a channel has complex geometry or is made of hybrid materials,even the flows include bubbles or droplets,how to calculate the drag forces of flows in a microchannel? 2 Shear forces.The shear flows can be used to lift a particle or a cell attached on a wall.But when a particle has a certain volume or a cell shape is deformed,how to decide the shear force on a particle or the interaction forces between the cell and the wall? We try to give a summary of the current results to discuss questions above.