The experimental study of beat frequency signal envelope extraction based on single-cavity and dual-comb was carried out. A piece of polarization-maintaining fiber (PMF) with strong birefringence was introduced into a single fiber laser to make the pulses multiplexed and mode-locked in two directions with orthogonal polarization. By finely adjusting intracavity polarization states, the continuous adjustable dual-comb generation was realized in the range of 337 Hz~2.33 kHz. The dual optical frequency combs with extinction ratios of 28.5 dB and 38.2 dB were obtained by laser extra-cavity polarization states regulation and polarization beam splitting. After asynchronous sampling of the dual optical frequency combs, the designed envelope detection circuit was used to extract the envelope of the beat frequency signal. Compared with the results of envelope extraction algorithm based on spline interpolation and Hilbert transform, the extracted peak position of the envelope was basically consistent, which verified the feasibility of the method. The experimental study of dual-comb beat frequency signal envelop extraction can quickly extract envelope shape and envelope peak position in real time, which can be further applied in the fields of envelope signal triggering and precise ranging.