This paper presents a fast adaptive time-frequency method for analyzing stationary and nonstationary vibration signals with transients. The method is developed based on instantaneous frequency (IF) – variations in the time domain. The variable window length is determined by estimating the local IF in every window slice over time. The proposed method is tested using simulation signals and experimental vibration data. The results show that the proposed method can successfully retrieve transient signals at a 3 dB signal-to-noise ratio, and improve stationary and nonstationary signal resolution in time and frequency domains. The proposed scheme offers better resolution compared to the standard short-time Fourier transform (STFT), and the computing cost is only slightly greater than STFT scheme.