Based on the introduction of differential oscillator fundamental, the influence of noise on the oscillator phase diagram is analyzed emphatically, and the linear relationship between the phase diagram size and signal amplitude is derived to make up for the shortage that differential oscillator can’t detect the signal amplitude, the setup principle of oscillator system parameter is also presented. The theoretical analysis, simulation test and engineering application show that this method is simple and robust, and has a good anti-noise property, the weak fault signals can be detected from the strong background noise, thereby providing a visual detection method for the incipient fault diagnosis of mechanical equipments.