Aiming at the problem that the amplitudes of false targets (FTs) are correlated among receivers in multistatic radar system (MSRS), a multi-jammer cooperative deception jamming method based on periodic multiple phases modulation (PMPM) is proposed. A FT string with random fluctuations in amplitude can be generated after the signal undergoes PMPM. In the distributed jammer system, each jammer adopts PMPM jamming method with different parameters, and then jointly transmit beamforming to forward jamming signals. Finally, the amplitude of the FTs between receivers is jointly affected by the azimuth angle and the phase modulation coefficient, which destroys the amplitude "coherence" of the FTs between receivers, and eliminates the amplitude symmetry and high-order attenuation characteristics of the FT strings generated by traditional jamming method. We study the amplitude compensation and amplitude correlation performance of the proposed jamming method, derive the rank of the ratio matrix of amplitude correlation factors, and prove that FTs have dispersiveness in the amplitude ratio space. In order to obtain the optimal and stable jamming effect, a genetic algorithm (GA)-based jamming modulation parameter optimization method is designed, which effectively drops the discrimination probability of physical targets (PTs) to 14% in the benchmark scenario. Simulation experiments demonstrate the feasibility and effectiveness of the jamming method.