Because the shortwave differential frequency hopping（DFH） system used in military communications will be exposed to hostile multitone jamming inevitably

the jamming model for DFH system is proposed.The performances of DFH system in both additive white Gaussian noise channel and Rayleigh fading channel in the presence of multitone jamming are analyzed by means of the Union-Chernoff bounding technique

and the bit error probability upper bounds are derived.The RS channel encoding technique is also employed in the system aiming at the error floor problem in Rayleigh fading channel when the bit error probability is 10

-3

.Numerical result shows that the system with coding offers a better performance and a coding gain about 7 dB is achieved in Rayleigh fading channel.