The analysis and evaluation of jamming becomes very important with the strain of spectrum resources and the intensification of electronic countermeasures. In order to deepen the understanding of the mechanism of multitone jamming (MTJ) on multiple frequency shift keying and frequency-hopping (MFSK-FH) system, as well as support the communication equipment to improve the anti-jamming ability, the optimal MTJ pattern for a MFSK-FH system is analyzed in this paper. Firstly, the incoherent demodulation receiving model of MFSK-FH system under MTJ is established. Then, the optimal jamming channel, optimal jamming phase and optimal jamming tone number are discussed in detail. Finally, the simulation results of bit error rate (BER) performance are given.