Abstract: The reservoirs in Mawangmiao oilfield is strongly sensitive and acid sensitive because of its ferreous minerals, such as pyrite and illite/smectite mixed- layers. The injection water quality is not eligible for a long time, which has led to solid invasion and oil jam in the formations. Scale analysis indicates that the scale mostly consists of calcium carbonate, a little of iron scale and magnesium carbonate. On the basis of the plugging mechanism, an acidizing fluid--the MHB chemical retarded acid which can use appropriately in Mawangmiao oilfield has been developed. Laboratory studies indicate that MHB chemically retarded acid can flush oil, inhibits the swelling of clay solids, prevents the deposition of iron ion and has a good effect on the blocking remove of oil and Fe3 + deposition. At the same time, it has minor corrosive to the pipeline, has good compatibility with the oil, and doesn't form acid sludge, so it can be used as the optimal formula of blocking removers in the oilfield