The effect of the traditional weak signal detection on low SNR is undesirable. this paper proposes an improved method for the detection of the weak signal under strong noise background. It replaces the nonlinear restoring force of a chaotic system by a equation of -x5+x7 by means of a single Duffing oscillator. Compared with the traditional Duffing oscillator detection system, this method performs stronger robustness. It states the working principle of weak signal detection based on the phase plane changes, and any unknown weak periodic signal detection can be achieved through the conversion of the time scale. The simulation study on the weak periodic signal detection under the noise background is also carried out, and verified against the detecting results of the real bearing fault signal. It is found that the proposed method obtains good effect. It provides a reasonable method for the engineering application.