At some old oilfields such as Dagang,the macro-pore formed in the long - term flood development,decrease the sweeping efficiency and increase the difficulty of EOR.Using PH-PAM cross linked with composite cross linking agent A as gelatin,which formula is that the molecular weight of 1.0 106,1%-3% PHPAM and 0.8%-1.4% of composite cross linking agent A.This blocking agent can keep stable at least 5 months in the reser-voir environment of 80?,13454 mg/I degree of mineralization.Also,it can block off the pore of high penetration core over 95% and its intensity at least 25 MPa/m.So,this blocking agent is fa-vorable for the water plugging of macro-pores.