Reinjection into reservoirs to displace oil is an environmentally friendly and efficient way to treat and use produced oily sewage. However, the permeability damage to the reservoir by the small oil droplets in the oily sewage (usually called oil-in-water, OIW) is a huge challenge in oil industry. In this work, microfluidic device is designed to qualitatively and quantitively evaluate the OIW damage using both micro-homogeneous model and micro-heterogeneous model together with core flooding experiments. The results show that OIW can cause serious permeability damage (more than 60%) to the porous media after 50 PV sewage injection due to the adsorption and accumulation of oil drops in four main forms: oil droplet blockage, column oil blockage, cluster oil blockage, and blind oil blockage. To relieve the OIW damage, according to the composition of oil in the produced water, a new oily blockage removal system, which is composed of organic solvent, surfactant, and alcohol, is developed to solve the problem of pore blockage caused by OIW. The three components in blockage removal system cooperate with each other can effectively remove the blockage in pores caused by OIW, and the permeability recovered to more than 96% of the initial permeability values after 20 PV injection of blockage removal system.