In order to satisfy the performance requirements of gel material used in snubbing service，the viscoelastic polymer gel plugging system was developed using acrylamide，sodium methacrylate，heat-resistant amine monomer，ammonium persulfate，polymer LAH，crosslinking agent MEN&PLE and toughening agent CAL as raw materials. The effects of initiator，simulated oil，salt and reaction temperature on gelation time of liquid and strength of gel were investigated by employing the thicken tester of high temperature and high pressure which could simulate the real environmental strata well in laboratory. The experiment results showed that the high strength gel with the intensity up to 30 N and pressure capacity about 2 MPa/8 m formed in a wide range of pH 7—13 and reaction temperature 40—130℃. Meanwhile，the gelling time and gel strength could be adjusted by changing the dosage of initiator. The viscoelastic gel had good stability and strong contamination resistance. When the dosage of simulated oil was as high as 20% or the dosage of Ca²⁺ or Mg²⁺ was 15×10⁴mg/L respectively，the gelling property of viscoelastic gel was good.