Abstract: Since the large-scale development in 1997,Chang-2 reservoir of Zichang Oilfield has mainly been produced under natural energy drive.With time going by,the formation pressure declines step by step and the oil reservoir near the well area is getting more and more foul,which causes the pump to be stuck and even off production.As a result,the output of oil wells decreases a lot.Based on analyzing the reservoir mineral composition in this area,this paper selects and optimizes the acid system by using such compositions as hydrochloric acid 10%,glacial acetic acid 2%,fluo boric acid 3%,hydrofluoric acid 2%,anti-corrosive agent 1%,active agent 1%,cleanup additive 1%,clay stabilizer 2%,ferric ion stabilizer 1%,antiswelling agent 1.5%,paraffin remover 1%.The result of the experiment is satisfactory.The new technology is applied in 88 wells in the blocks of the oilfield,such as Block Yujiaping,with the efficiency of acidizing and shutoff removing achieving more than 75%,the oil recovery from the average single well enhancing by 39.6 t,and the term of validity being about half a year.The new technology features in simplicity,low cost,and high efficiency,which has been one of the major measures to reconstruct Chang-2 reservoir in recent year.