Duffing equation is a kind of important power system. Aiming at modulation and demodulation of chaos parameters in this system, firstly, a new modulation system of Duffing parameter is established in this paper by controlling constant parameters based on threedimensional Duffing system. Secondly, mathematical expressions are designed according to the probability of chaotic state appearing at two centre points. This kind of demodulation method has the advantage of realizing digital information demodulation without synchronization of transmitreceive system. Lastly, demodulation results and the new running track of Duffing system are given in this paper. Simulation results show that this new system can effectively realize modulation and demodulation of digital information under the chaotic state unchanged.