Traditional Duffing oscillator detection method is set too complicatedly and has many restrictions. In order to detect the weak subsynchronous resonance signal quickly and accurately, based on the basic principle of subsynchronous resonance, this paper presents a varying scale and comprehensive scanning Duffing oscillator subsynchronous resonance detection method. Through the introduction of the coefficient of scale, a large-parameter signal detection is achieved. By using the comprehensive scanning method, the detection dead zone of the initial phase angle is eliminated. The simulations of sub-synchronous resonance detections with different signal-to-noise ratios are conducted. Results show that the method has a wide detection frequency range, good noise immunity and high accuracy of weak signal detection.