Abstract: In this paper,it developed DL07 series plugging agents,optimized plugging formula and dosage suitable for different size of leakage channel and its mechanism are discussed.In-door experiment results showed that:the optimal dosage of DL07-1 is about 2% for 0～0.5 mm leakage holes,the optimal dosage of DL07-7 is about 4% for 0.5-1 mm leak-age holes and the optimal dosage of DL07-10 or DL07-12 is about 6% for 1～2 mm leakage holes.The pressure containment is enhanced 3.5 MPa by those above.These sealing agents have a good compatibleness and take less effect on the performances of drilling fluid.These leakagetightening and caulking technology were used in A31-112x well of Erlian oilfield and two wells were sealed successfully.