Abstract: The injection wells in the sandstone reservoirs in the Changqing Oilfield were affected by many factors including reservoir physical properties and water quality,resulting in increasing high-pressure and under-filled wells.Conventional acidizing and injection technology have a complicated process and their term of effective performance is very short.In order to improve the effect of acidizing and injection,to simplify the operation process,and to reduce the treatment time,we proposed a COA-1S acid fluid system for texts of the acid system ratio test,core flooding and corrosion inhibition performance.This system exhibits good retardation,anti-corrosion and chelation performance.The chelate acid pulse injection and acidizing stimulation technology were developed by means of a process of technique optimization,which integrates hydraulic pulse technology with the acidizing and injection technology.This technology has the advantages of immobilizing the string,does not require pressure relief,and there is no reverse discharge.This chelate acid pulse injection and acidizing stimulation technology for immobilized string of injecting well were been applied to three wells and times,with effective efficiency up to 100%.The average water injection pressure was decreased by 9.2 MPa after acidizing,and water injection volume for single well was increased by 12.3 m3/d,with quite good results.The field application demonstrated that the technology has an obvious effect in reducing pressure and increasing injection,which solved the problems of conventional acidizing technique in complex acidizing treatment process and a long well occupation time.It possesses good application and promotion prospects.