Abstract: Frequency-hopping(FH) is widely used in many ways. FH communication is a kind of communication system with strong anti-jamming capability. This paper discusses a new algorithm to block FH communication system by using pulse-jamming signal. Meanwhile, jamming effects of pulse-jamming signal on synchronization to FH communication system is simulated in MATLAB. The simulation results show the validity of pulse-jamming on FH communication system and jamming energy can be effectively reduced by attacking synchronization of FH communication system.