Abstract: The relationship between polyacrylamide structure and salt resistant capacity was analyzed, and a new gel type plugging agent with cationic polyacrylamide (CPAM) as main agent and with high salinity resistant capacity was developed. Resin with benzene ring structure is taken as crosslinker, and protectant is added to decrease the hydrolysis of main agent. Experimental results show that this agent can plug the formation water with NaCl salinity of 220 000 mg/L and CaCl2 of 10 000 mg/L below 85 ℃. Optimal pH of the plugging agent is 7~11.The breakthrough pressure measured by cores is more than 45 MPa/m. For continuous injection of 20 PV water after breakthrough, plugging strength is still more than 30 MPa/m, with plugging rate of 98%. The plugging agent has long period of validity under high salinity. It also has selectivity, since plugging strength is low for the layer of high oil saturation.