Abstract: In the field of covert communications, chaotic pulse-position modulation (CPPM) and chaotic pulse-width modulation (CPWM) have been developed rapidly. Compared with the traditional pulse-bit modulation (PPM) and pulse width modulation (PWM), chaotic modulation achieves the better communication concealment, but the communication rate is still not improved. Based on the CPPM technique, a new chaotic pulse-position and pulse-width joint modulation (named ‘CPPPWM’) communication system for underwater acoustic communication is proposed, which has the characteristics of double concealment. Compared with the CPPM and CPWM communication system, the joint modulation has better concealment, higher communication speed and greater effective bandwidth. In this paper, the CPPPWM underwater acoustic communication system is studied and realized by Tent mapping. The characteristics of the system, particularly the bit error rate are analyzed, and the bit error rates of the joint modulation system obtained from the theoretical calculation and simulated test verify the validity of the CPPPWM communication system.