The invention relates to a LNG storage tank perlite settlement monitoring system and method based on distributed optical fibers. The system is characterized in that it comprises a plurality of distributed temperature-measuring optical fibers, an optical fiber junction box, a distributed optical fiber temperature-measuring host computer equipped with at least two channels, and a display screen host computer; respective distributed temperature-measuring optical fibers are laid on the inner wall(s) of one or more LNG storage tank outer tanks; the head ends and the tail ends of respective distributed temperature-measuring optical fibers are connected with the optical fiber junction box; the optical fiber junction box is connected with respective channels of the distributed optical fiber temperature-measuring host computer via the distributed optical fibers; and the distributed optical fiber temperature-measuring host computer performs dual-channel bidirectional transmission and demodulation on the head ends and the tail ends of respective distributed temperature-measuring optical fibers to obtain a final temperature measurement value, sends the final temperature measurement value to the display screen host computer for display via a TCP/IP communication interface, and sends the final temperature measurement value to a centralized control system for further processing via a standard communication interface. The system and method can be widely applied to the monitoring of LNG storage tank perlite settlement.