The problem of producing both oil and water is caused by long-term waterflooding in the fractured-cavity carbonate reservoirs. To solve the problem，low molecular weight polymer was used in this paper to replace high molecular weight polyacrylamide which was commonly used as blocking agent，and novolac resin used as crosslinker. The effects of dosage of polymer and crosslinker on the viscosity，gelation time and gel strength were investigated，as well as high temperature and salt resistance. The results showed that with the increase of polymer dosage and crosslinker dosage，the viscosity of the system increased，the gelation time shortened and the gel strength enhanced. The results of TG and DSC indicated that the system had good thermal stability. The system had good temperature-resistance and salt-resistance. The gel product，prepared with 4.8% of P（AM-co-AMPS）and 10% of phenolic resin，did not degrade when soaked in the simulated formation water with the mineralization of 22×10⁴ mg/L for 48 h at the temperature of 120℃.