Abstract: Proposes novel method—the chaotic pulse amplitude modulation to implement ultra-wide band(UWB) direct chaotic communications. The implementation of chaotic pulse amplitude modulation(CPAM) and demodulation is described. The sporadic-coupling synchronization methods for the UWB system based on CPAM are simulated with electronics workbench(EWB). Means of the synchronization are confirmed by the simulation results. The simulation result for the probability of bit error showed that the performance of CPAM was worse than traditional methods such as quadrature phase shift keying(QPSK). However the introduction of chaotic signal much improves security of communication.