Laser Doppler vibration measurement mostly uses laser heterodyne method, which requires orthogonal mixing, filtering, and arc tangent operations in the demodulation process, and the demodulation process is very complex process with high hardware requirements. In this work, we propose a spectrum analysis method based on laser Doppler carrier signal, which uses the intensity relationship between the carrier main frequency and the side frequency caused by vibration signal to directly resolve the amplitude and frequency information of vibration target, and its maximum detectable amount is not limited by the conventional heterodyne demodulation limit. The feasibility of the method is further verified by simulation and experimental study. In the benchmarking experiment with the standard vibration sources, when the distance from the vibration target is 17 m, and the vibration target frequency range is 60 Hz–20 kHz, the measured amplitude range of the scattered light signal is 21.44 pm–44.21 μm, showing excellent demodulation consistency with the reference value. It is indicated that the spectrum analysis method proposed in this work can be applied to non-contact long-distance measurement of smooth vibration signals.