Abstract: chaotic oscillator could detect extremely weak signals, and has many advantages. Weak signal detection based on the chaos theory put forward a chaotic oscillator duffing applied to the triple-state pulse position modulation signal detection in this paper, first of all the driving force was adjusted in the detection process, and made the system in the critical state of from a chaotic state to the big cycle, at this point the threshold of the system driving force was ,and the phase trajectory was still chaos, when the triple-state pulse signal was added in the system, the system turned into a state of large-scale cycles from chaotic state, was detected a periodic signal in the input signal; if the system continued to be at a chaotic state, it indicated the input signal was the pure noise; finally the signal envelope was extracted through coherent detection and achieved the triple-state pulse signal detection. The simulation results shown that the method referred in the text was the feasibility and effectiveness.