Dual-source jamming is an effective monopulse radar jamming method. The jamming effect is analyzed under the condition of single echo. But in the actual situation, pulse accumulation is utilized in signal processing which would affect the phase between the dual-source jammers and finally affect the dual-source jamming effect. Simulation analysis indicates the deception angle of monopulse radar under dual-source jamming fluctuates in some range instead of keeping stable.