Adaptive nulling technology is one of main anti-jamming measures adopted by GPS receiver.In order to force adaptive nulling invalidation, on the basis of analysis of PI algorithm applicability for adaptive nulling of GPS receiver, in view of the characteristics of PI algorithm including less prior information required, slower convergence rate and wider nulling angular region at low JNR, countermeasure scheme proposed is that weak jamming entrance covered by strong jamming, weak jamming clearance filled under strong jamming synchronous on-off and jamming pitch direction approximation.Simulation results validate feasibility and effectiveness of the proposed countermeasure scheme.