The deterioration of treated oilfield injection water quality in the distribution system has become a common issue that hinders the application of oilfield wastewater as a reusable source for oil production. Hereby, this work devotes to monitoring treated water parameters and the formation of pipe scales in the whole distribution system in Jianghan oilfield. Our results showed that the cause of water deterioration in the distribution system is due to the increased suspended solids. Coupon tests indicated that the rates of pipe corrosion and scale formation significantly increased, which was in line with our monitoring data. This further demonstrates that the deterioration of injection water leads to significant pipe corrosion and scale formation after the long distance transportation from effluent wastewater treatment plants to injection wells. The chemical composition of the collected pipe scale is consistent with that of suspended solids extracted from water samples. This indicates that the increased suspended solids in water are likely due to the contribution of pipe scale that can be on the walls of pipelines, consequently deteriorating the injection water quality. The findings of the present study show an important significance in understanding the mechanism of injection water deterioration in the distribution system.