Micro flow experiments in microtubes with nominal radius of 5μm have been accomplished and the impacts of wettability on micro flow have been studied. Method of improving injection by resistance force reducing agent has been discussed in this paper. Research results show that the flux differences between hydrophobic and hydrophilic microtubes represent more obvious at low velocity and low pressure condition. Water flux in hydrophobic microtubes are higher than in hydrophilic microtubes when the pressure gradient is smaller than 1 MPa·m-1, but the differences are no more obvious when the pressure gradient is greater than 1MPa·m-1. Some surfactants (resistance force reducing agents) can be adsorbed and arranged tightly on the wall of the microtube, and the wettability of the wall surface can be changed in a certain extent. Thus, the attraction of wall to water molecule is decreased, the effective boundary layer is getting thinner and the flow resistance can be reduced as a result. Based on this research, it is foreseeable that resistance force reducing agents can be applied in low permeability reservoir to improve water injection and improve oil recovery.