The invention discloses a swinging vibration measurement device based on distributed optical fibers, and a demodulation algorithm. The device is used for monitoring the swinging amplitude, frequency and position of a line in real time, and comprises an optical path unit and an electronic unit. The optical path unit enables an optical path on the swinging line to be modulated, and the electronic unit enables the optical path information to be demodulated in real time. The device employs a coherent light source with a small line width and lower frequency drift characteristics, and the optical fibers are continuously distributed in the line, thereby achieving the real-time measurement of a continuous space of a measured object. The device can monitor the swinging state of a line tested by an indoor swinging testing machine in real time, can timely obtain the real-time data at each swinging frequency and carry out the data accumulation, and lays a foundation for the long-distance monitoring of an outdoor real test line in future.